Postfix, Dovecot, MySQL :: Name does not exist

I have followed these two guides to (install and troubleshoot) Email with Postfix, Dovecot, and MySQL but……

The result

• local mail seems to work

• interaction with remote mail - sending and receiving - does not work consistently

• I can connect using pop3 over a secure connection but with the same result

Examples

• name@local.com will send to, and receive from, itself

• alias1@local.com (an alias for name@local.com) will send properly

• name@local.com will send to name@remote1.com but will not receive from it

• name@local.com will NOT send to name@remote2.com nor will it receive from it.

Again, the results are the same locally and with pop3.

It is worth noting that both the remote domains are in this case forwarders

Note. I have used local.com and remote.com (here and below) to clarify source and destination. I have not actually used those names. Please read them as example.com.

Errors and messages

In the case of the remote example that will NOT send, the error message is 550 the name does not exist.

As per the troubleshooting guide…

doveadm user name@local.com

… gives good results, but running it on a system user does not….

doveadm user user1
field value
uid 1000
gid 1000
home /home/user1
mail maildir:/var/mail/vhosts//user1/
system_groups_user user1

My understanding is it should say user does not exist. I have been unable to figure out how to correct this.

MySQL is basic

virtual_domains = local.com

virtual_users = name@local.com and passwd

virtual_aliases has two…

-- alias1@local.com -> name@local.com (works)
-- alias2@local.com -> name@remote.com (does not work)

Something on the "Email with Postfix, Dovecot, and MySQL" page is not clear to me. Namely…

re: 9. Update the /dovecot-sql.conf.ext file with your MySQL connection information

Near the end of that section is a part that says…

• To use an alias as the username: Add the alias as the source and destination email address to the virtual_aliases table, and adjust the password_query.

This is the part that is not clear.

If the source and destination addresses are the same in the virtual_aliases table, does this mean… an alias has two source entries in the virtual_aliases table? One that functions as an alias and one that functions as a logging credential? If not, how would the server know where to send the alias. If yes, how does it know which to authenticate and which to send?

If I use the alias password_query, will ordinary virtual users still be able to use mail? If so, why not use the alias query and be done?

I would like to see an example of a virtual_alias table and a virtual_users table configured to use a virtual and an alias as usernames.

While we're here…

There is an inconsistency between the main guide and the troubleshooting guide. The mail_location is given two different ways.

Install guide has…

mail_location = maildir:/var/mail/vhosts/%d/%n/

Troubleshooter has…

mail_location = mbox:~/mail:INBOX=/var/mail/%u

Which is correct?

To this point, I "surmise" postfix is verifying destinatin/remote email names locally rather than remotely/internetly. At least the core components seem to be working as expected. But something is amiss. Hopefully nothing catastrophic. I am tempted to say a whitelist would fix this but then I wouldn't be able to receive from addresses not already in the list. Lastly, I do not require system users to have access to email. In fact, I'd rather not have system user email at all.

I have spent a couple days reading about this problem - seems it's a common one - but I can find no consistent, predictable solutions that have solved it for me.

I welcome the benefit of your insights and experience. Thanks for reading this far.