In some very weird situations, a normal local mailbox sending a normal email can be marked as spam, probably because of postsrsd (T1099: Install postsrsd on gargantua.reyboz.it to fix the SPF mailforward shit) as default rewrite all emails and DKIM has issues with that.

Reported by https://t.me/itwikicon/2236

I documented myself in:

• https://github.com/roehling/postsrsd/issues/42#issuecomment-149690471
• https://serverfault.com/questions/706227/only-enable-srs-when-forwarding-to-enable-dmarc/780367

And I've opted for this solution:

sender_canonical_maps = mysql:/etc/postfix/mysql/mysql-email2email.cf, tcp:localhost:10001
sender_canonical_classes = envelope_sender
recipient_canonical_maps = tcp:localhost:10002
recipient_canonical_classes= envelope_recipient,header_recipient

Plus

# this was already installed
sudo apt install postsrsd
systemctl reload postfix

And now it seems that outgoing emails are not marked as SPAM. Tested with a real-life email to the original reporter.