I hope we have some email hosting guru here.
My system use ubuntu 20.04 and keyhelp control panel.
Installation goes well, /var/log/mail.log don’t provide much info.
Server use postfix and doveconf.
But, if i send extrenal email (gmail, outlook…) it will stay in email queue.
Sending email for domain that is hosted inside keyhelp work well .
And here is doveconf: Untitled - Pastebin
Email log: Untitled - Pastebin
Postfix logs says Connection timed out, so probably firewall blocking outgoing port 25 or some server providers blocks outgoing 25 to help prevent spam.
What Razza pretty much said.
Maybe even check to see if your IP is on a blacklist (https://mxtoolbox.com) because sometimes (who knows) people might just drop your IP completely.
More than likely your provider is blocking port 25.
Many providers do this because email spam is frowned on to such a significant level.