How to prevent an email address from receiving mail (noreply@example.com)

Cisco30

Hi
I created an email address like noreply@example.com to send information to my users of various services (Plex, Overseerr, Nextcloud, etc.). How can I block the receipt of emails to this email address and only allow sending?
Thanks.

esackbauer

I guess you did not create an “email address”, but a mailbox with that principal noreply address.

For such services I do not use a mailbox, so this noreply address does not exist anywhere in mailcow, mails to this address will be bounced.

But you can still use any sender address like whatevername@example.com or noreply@example.com.
Simply set your services to use port 25 of mailcow (requires no authentication), and in mailcow admin UI configure those IP addresses which run those services as “forwarding host”.
So you are basically using mailcow as a relay server, and this will work as long as you send mails with any of your domains configured in mailcow.
If you send to external mail addresses it could be a little more tricky, and might require additional work, because such relayed mails are not DKIM signed by default.

Cisco30

@esackbauer
Thanks for your help.
Yes, I did create a mailbox, not an email address. ^^
I tweaked the process to stop receiving emails and continue sending with DKIM and SPF by changing the mailbox size to 1MB, then I overloaded it with an email.

and now when I try to send an email, even without any subject, I get a “Mail Delivery System”
.```
..
Action: failed
Status: 5.2.2
Remote-MTA: dns; dovecot
Diagnostic-Code: smtp; 552 5.2.2 noreply@example.com Quota exceeded (mailbox
for user is full)
…

It’s not very clean, but it works…
Do you think it could cause sending problems later? For now, sending emails works well with my services (Nextcloud, Oversseer, etc.), and these services don’t create emails in the “Sent Items” folder.

esackbauer

I wouldnt bet that is stays like this. Maybe a dovecot update might change behaviour. I prefer a clean solution 😉