Nothing ever seems to go straight forward for me.
I’d originally set up a mailbox in cPanel to catch email at email@example.com but then I decided that I’d rather just forward it to another address instead to save checking multiple inboxes.
Turns out cPanel didn’t like that.
I set up the email forwarder which worked perfectly, but oddly users sending mail to the firstname.lastname@example.org were getting a bounceback error, despite the forwarder actually working.
Thankfully after taking a look into it the fix was pretty easy. Turns out cPanel hadn’t properly deleted the original mailbox.
So to fix it I just FTP’d into /home/user/mail/domain.tld/
And then renamed the user account that was in that folder to user-bak.
Tested it again & it worked fine.
Now, I could go back in & delete the folder as it seems to be working… But I’ll just leave it renamed as bak in case any problems arise so that I can easily switch it back.