I've had to book a few flights with BA recently. Up until a couple of weeks ago their acknowledgment e-mails came through fine. And then I stopped receiving them. Taking the time to delve in to the mail logs yesterday I noticed this:
Aug 20 07:47:45 jc sm-mta: l7KElEmk015347: ruleset=check_mail,
reject=553 5.1.8 website +LHS=RHS@bounce.baplc.com...
Domain of sender address website+LHS=RHS@bounce.baplc.com does not exist
(I've redacted the left and right hand side of the actual e-mail address it was being sent to)
If that's just so much gibberish to you, it says that BA are sending e-mails with a return path of ...@bounce.baplc.com. Working through the logs shows that they've been doing this for some time.
But at some point in the last few weeks, someone at BA has removed the bounce.baplc.com entry from their DNS. So my, and countless other systems around the world, will begin rejecting messages.
This rejection is quite correct. Since bounce.baplc.com doesn't exist, my system (and any other system with the same configuration) will have nowhere to send any bounces that might occur. And sending messages from domains that do not exist is also an exceedingly common spammer tactic.
I've used the "Report problems with our site" feature to report this to BA, but I don't have high hopes of anyone listening.