I've done what I can, but Expedia (whom I have never contacted in any way whatsoever, ever) have apparently sent us a sales email which now seems to be trapped into an endless spiral.

Earlier today I black-listed the precise email address on all our email addresses, then blacklisted their entire domain.

Yet every time I Get Mail, there they are again, dozens of them, with increasingly long headers such as:

From: travel@customercare.expedia.com
Subject: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Your email requires verification - Case ID : [REQ:M-4933303]

How to get out of this craziness? Stupid emails requesting verification are bouncing backwards and forwards endlessly and all reporting to me. Will this go on for ever, or only until either their server or mine gives up?

Yes, I know. It's not TEOTWAWKI, but is extremely irritating when I've done my best at this end.

Thanks in advance.