Cant get email to work on my instance

I cant get my email sending to work on my instance. After trying for hours, i wanted to ask for some support here since im quite stuck and dont understand.

I installed Lemmy using ansible so everything is set up in a very standard way - except email.

I want my instance to send email to an external smtp server (Fastmail) whenever there is a need to send an email (user registration, password reset, etc).

Currently the email settings in lemmy.hjson looks like this:

<pre style="background-color:#ffffff;">
<span style="color:#323232;">  email: {
</span><span style="color:#323232;">    smtp_server: "postfix:25"
</span><span style="color:#323232;">    smtp_login: "abc@fastmail.se"
</span><span style="color:#323232;">    smtp_password: "fastmail_user_password_here"
</span><span style="color:#323232;">    smtp_from_address: "noreply@lemmy.today"
</span><span style="color:#323232;">    tls_type: "tls"
</span><span style="color:#323232;">  }
</span>

It seems like i need to have postfix:25 as the smtp server. What i really want is to put smtp.fastmail.com:465 here since thats what i want to use to send email. But that doesnt seem to work.

So I understand I need to send email through postfix, but then I wonder, how should the config look like to send emails to smtp.fastmail.com on port 465 (which is what they have on fastmail), with a specific username and password used on the fastmail server?

I think a lot of people are having issues with the email part of the setup, judging from the many reports of spinning buttons on user signup… this is a very likely reason, specially since there is no error message to the user.

Please help me sort this out, how should i configure this?

EDIT:

Ok after a lot of experiments and help from people below, this was the solution.

<pre style="background-color:#ffffff;">
<span style="color:#323232;">  email: {
</span><span style="color:#323232;">    smtp_server: "smtp.fastmail.com:587"
</span><span style="color:#323232;">    smtp_login: "my_email@fastmail.com"
</span><span style="color:#323232;">    smtp_password: "password"
</span><span style="color:#323232;">    smtp_from_address: "my_email@fastmail.com"
</span><span style="color:#323232;">    tls_type: "starttls"
</span><span style="color:#323232;">  }
</span>

Using this, email sending finally works. I couldnt use something else in the smtp_from_address. Which means my real email gets shown to users, so I will probably create another email address for this purpose completely.

Also specific to Hetzner instances, they dont block port 587 so you can use that with starttls.