Comments on Postfix - do not list domain example.com in BOTH mydestination and virtual_mailbox_domains

you mention that to solve the problem, you need to make both different, but never went far enough, nobody knows how to fix the problem, just that there is a problem. the error message already explained the problem, therefore in order to be a "howto" we need to know "howto" fix it.

That would depend on how the server is set up.  There is no one-size-fits all solution.  It's different for every configuration.

In my case, at least, removing mydomain.com from mydestination cleared things up. On my server, mydestination is just localhost, localhost.localdomain

GREAT SOLUTION, works for me.

This worked for me also.

The solution is as simple as you mentioned.  it is working.......   :)

I see that this is old but there is a step that may help someone moving forward:

If you edit /etc/postfix/virtual don't forget to rehash it by running 

# postmap /etc/postfix/virtual 

Otherwise the virtual.db will be older and postfix won't see it.

Great! I could fix this issue.

Thank you

perfect, I could not find the solution. It only remains to make ispconfig accept 10MB email, modify the /etc/postfix/main.cf ... message_size_limit and virtual_message_size but in webmail it is still 2MB  

well, it would be much better if you gave some examples of what you can do, and explain why you shouldn't use it in both, now you're only explaining what we already knew; Don't do it