--- title: Send emails when receiving a comment - Ruby on Rails slug: send-emails-when-receiving-a-comment-ruby-on-rails published_at: 2021-09-03 14:00:11 +0000 updated_at: 2026-03-04 20:13:57 +0000 summary: description: In this episode, we'll send an email to a post or comment author when a new comment is added to their original content. #rails #rubyonrails tags: [cjav_dev, web development tutorials, web development for beginners, vim, ruby, rails, javascript, sending email, letterr_opener] views: 2509 author: CJ Avilla url: https://www.cjav.dev/videos/send-emails-when-receiving-a-comment-ruby-on-rails youtube_url: https://www.youtube.com/watch?v=Y4-qcXdhPvY youtube_id: Y4-qcXdhPvY embed_url: https://www.youtube.com/embed/Y4-qcXdhPvY thumbnail_url: https://i.ytimg.com/vi/Y4-qcXdhPvY/hqdefault.jpg type: video --- # Send emails when receiving a comment - Ruby on Rails *Published: September 03, 2021* *Views: 2509* ## Watch [Watch on YouTube](https://www.youtube.com/watch?v=Y4-qcXdhPvY) [![Send emails when receiving a comment - Ruby on Rails](https://i.ytimg.com/vi/Y4-qcXdhPvY/hqdefault.jpg)](https://www.youtube.com/watch?v=Y4-qcXdhPvY) ## Description In this episode, we'll send an email to a post or comment author when a new comment is added to their original content. #rails #rubyonrails ## Transcript hey what's up welcome back in this episode you're going to learn all about sending emails when we uh first receive a comment on our blog posts so we're talking about sending emails today we actually went over sending email in a previous episode previous couple episodes so if you are curious about sending with send grid you can head over and take a look at those today we're just going to use a letter opener and we want to get the process for sending some outbound emails when comments happen on our blog so what we're going to do here is we're going to say railsgmailer we're going to call it the comment mailer i think and we're just going to have you know a message that's sent to the author of the blog post when they receive a post or when they receive a comment and then maybe we'll also in the future send a an email to the author of a comment when the comment is replied to so when we generate a mailer it gives us a couple different things so first we get a mailer class we also get this view for the mailer and that's where we can write our html.erb templates for the html versions of the views we can also write text versions of the views that'll be sort of when we send a multi-part email it'll have the html version and the text version so let's just open up this comment mailer really quick and take a look at what we've got so right now it starts out as empty we can go over to application mailer which is sort of the the parent class here and we can see that by default we are coming from uh from at example.com and we're using the default mailer layout and i think that's an okay from address for now but i think in practice when we send mail about a post or comment we actually want to be a little bit clever about the from address or the in reply to and so we're going to just take a look at how we might just really quickly send you know a new comment message and that's going to be to the author like the blog post author so it might take in a user and then maybe their post or something uh and then maybe even the comment i don't know maybe we get in the the user and the new comment um and then we want to send this message so we're gonna use the mail method here and we're gonna send this to user.email and the subject is going to be just like a new comment on your post and then the content or the body is actually going to be rendered by by the view so we're going to just store the comment in an instance variable here comment and then we will go over to our views for the comment mailer and we'll add a new comment.html.erb template for the view and here we'll just say um like h1 congrats uh or like hey our heads up uh someone commented on your post and it would be nice if we included the content of the comment so we'll just say at comment.content and that should get us somewhat started i will need to play around this and test it out but what i wanted to do before we get too far is actually install this gem called letter opener so we're going to open up our gem file go down to development mode and say gem letter opener and we will bundle install to install that and this letter opener gem is super handy it allows us to test uh sending emails in test mode so we want to go to development to our development environment and like the settings in here and go down to our mailer our mailer settings okay yeah so delivery method is letter opener and perform deliveries is true so we need to set these two options in uh config environments development.rb and now let's see if we can fire up our rail server and then from the rails console let's try to actually send one of these messages so we're going to call the comment mailer dot new comment so we're going to say comment mailer dot new comment and these are class methods so they're they're like class methods directly on the class they're not instance methods for user.last and let's say the comment is going to be comment.last and that should that should create a new mail object but in order to actually send the mail object we have to say deliver now or deliver later we'll just say deliver now and here we see in the browser we see um this this uh new browser window popped open we can see a lot of information about the email that would have been sent so we can see that it's from from at example.com and it's about a new comment on your new post here's our our h1 and then this was the the actual comment um or the actual content that was in the comment that was posted so what we want to do is um when we receive a new comment on a post we want to fire fire off this email um so let's grab onto this code that we used the comment mailer new comment delivered now and we'll go over to our comments controller and when we create a new comment here so if we were able to successfully save it so let's say if we save then we want to do this so we the user is actually going to be um the the author of the post so we want to say author is equal to like uh at comment.post.user i think um let's see pose yeah that that makes sense and then um so this is going to be author and then the comment is going to be at comment and we will say deliver now now we might want to do something where we don't actually send this this email if the author is the same as the author of the comment so if uh author does not equal at comment.user um that way we're not sending an email message to ourselves every time we comment on our own posts maybe we'll just be like replying to someone else commenting on our post um okay so this should be uh sending the email message we're gonna deliver now in practice you want to deliver later and use a background processing but for now we're just going to use deliver now and that should be that should be fine so now if we go over to our application here and we pull up a post and we say uh let's create a new comment on this post this is a new comment that should fire an email uh i can't remember okay so we're logged in as wave at cjf dev i don't actually remember who the author of this post is but we will just submit this comment and hey look at that we got a new email so this was to cj villa gmail.com so the author of the post must have been cj available now we're able to receive comments or email messages and email notifications when someone comments on our post now what about the case where we're gonna like or i'm sorry we're gonna reply to another comment right because we can technically reply here so let's see does a reply also fire an email and we will say submit holy moly look at that it just works by default that's so cool um okay so there's a couple things we might want to change though right so there's this feature of some email services like this is a an email message from airbnb we have this airbnb that we host and when a guest writes in some content we have the ability to reply directly to that comment on airbnb by replying to the email and so one thing that's really common is enabling the ability to have someone reply from their email to a comment or to some message uh directly so that people don't have to install mobile apps sometimes or they don't have to go directly to airbnb or they don't have to go directly to the site this is also common for um like working with git there's a there's a bunch of other tools uh that do this that um that we might want to emulate but the idea is that like if you receive a comment or you receive a blog post i think even maybe reddit might do this too like you want to be able to reply directly to it from the email and so the way that works is the content of the email address if we look at the original here the content of the email has a reply to and the reply to has like a pretty name but then it also has like this email address where there's some unique identifier oh my gosh this one almost looks like it says whoa that's kind of cool um it has this unique identifier and it's the domain is a subdomain that's reply at but what really matters is being able to use this identifier to look up the thread or whatever the blog post or the comment that was sent to you in order to make it so that you can reply and so that your reply will be associated with that um with that content on the original site so what i wanted to do was just update our mailer so that the from address when we are sending these emails about comments um so the from address is has enough data encoded in it so that we could reply directly to the email and have that reply show up either directly on the post or direct or i'm sorry directly on the comment that it's in response to or in the reply that it's in response to so what i think makes most sense is to have this come from from something like comment dash and then maybe the id of the comment you probably want maybe at like in reply.example.com you probably want to use some like obfuscated key or some random id that's associated with the comment instead of some numeric id so that people couldn't use like an auto increment attack or something here but this should be fine so we're gonna the email address will actually look something like comment dash 12 at reply.example.com right and then we'll be able to use this 12 and we'll know that it's a comment so we can like look up the comment with number 12 and reply directly to that comment i thought about maybe having like the post id in here post like maybe comment 12 post one or something that way we can know exactly which post it was in reply to but uh i think if you think about it like the only time we're going to want to receive an email is if there's a comment happening on our post or on our comment we don't actually care necessarily if it is a um if it's a new post that we want to add a comment to it's like a completely separate use case so i think this is going to be fine 12 at reply.example.com and then um yeah i think that that should work that should work great so let's give this another another little whirl here and we will say we're gonna add a new comment another comment uh how's that from address look okay click submit all right and now check out that from address now we have comment dash 30 at reply.example.com so if we were to reply to this email and had some sort of tool to ingest the email address or like the inbound email we could extract this id and then use that id to look up the comment and then use the content of the reply to post a new reply to that comment directly so yeah this is kind of how you might send email as the result of receiving a post on or a comment now one thing i'm thinking about is are these comments or i'm sorry are the replies actually working as expected so i these were added by wave at cgive dev and they got sent to okay so let's log out and let's test let's do one test with a different email address here so let's go back to posts 11 and okay so the original was written by cgi of dev now if we reply to this one and say like from address looks great i would expect that submitting this sends an email to wave at cjf dead but let's just see if we got our logic right okay and no email was opened no email was opened so i think we got that wrong actually so let's go to our comments controller here and ah so we're looking at the post so we either need to look at the author of the post if it's a top level comment or we need to look at the author of the parent if it's a parent comment and maybe we want to send this new comment message to both right so like if this is a comment directly on the post we probably want to tell the post author but we probably also want to tell the comment author so maybe we want to say something like if at comment dot parent so if there's a parent parent dot user is the another author parent comment author maybe this one is like the post author and we'll just send two separate emails but they're they're gonna be the same basically the same content um and then here we'll say parent comment oops if the parent comment author does not equal the comment author then we'll send it to the parent comment author okay so we've got this one this is like uh send email to the original post author and this one is if this is a reply uh send an email to the og the oh comment the og comment author um okay let's see if that works so we'll refresh the page here and we'll say that we want to reply to um this one again say like from address looks great again and then we say submit and undefine local or variable or method parent this should be at comment.parent boom okay from address looks great again okay so this is i think this is now working as expected and the it did go to wave at cgi of dev which was the author i think of the parent comment yes okay cool all right so that is how we might send email as the result of receiving a comment on our post thanks so much for watching i think in the next one we might try to handle ingesting those inbound emails that are just directly in response to those messages so thanks so much for watching and we'll see you in the next one [Music] --- [Back to all videos](https://www.cjav.dev/videos) --- ## Hey Agent, thanks for visiting! 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