An in-use, legit, corporate email address is being rejected by FTH email servers

Hope you can help. When we use our "officers@..." or "members@" email aliases, the sender gets back an email with the following "not working" information:...<legit corporate email address>... appears to be an invalid or non-working recipient email address. (No advertised SMTP servers are accepting mail.) *** Please check the email address to make sure it is not misspelled. ***The email address being rejected is one of our members corporate email, which he uses to send and receive emails all day long in his role here at our company. Ours is a closed/corporate club, which should have no bearing on this issue. Also, non of the rest of us are having any issues. Furthermore, this member DOES receive the group email sent out via the "members@..." or "officers@..." email alias/list. It's very perplexing, and I hope someone here can help us fix whatever is happening here. 

The rejection email suggests posting here, if everything else checks out. Hopefully someone here can look into this. I'm not sure what all I should post here, as far as details or actual email addresses go. Please reply with any requests for further details. And thanks in advance!

Brian Rawlings
Treasurer
TECHnically Speaking Toastmasters

The email you gave me is working correctly.

Oct 5 22:31:12 toastmastersclubs sendmail[27888]: 295MVBCY027885: to=<adam.behman@techdata.com>, ctladdr= (501/502), delay=00:00:01, xdelay=00:00:01, mailer=esmtp, pri=121505, relay=mxb-00277801.gslb.pphosted.com. [208.84.65.207], dsn=2.0.0, stat=Sent (3k0hecy24x-1 Message accepted for delivery)

Thanks Brian. That was the mystifying part - it's a fully functional email that was producing a bizarre error reply to the sender, from FTH. And, it was only just that one email, out of all members who are on our corporate email convention.

I tried it again this morning, and no error message was returned from FTH, it's all acting normal now. Not sure if you did anything, or if - as is commonplace - a Klingon Bird Of Prey warship entered our system, decloaked, hit us with a tachyon beam, recloaked, and left. It's my best explanation for transient inexplicable behavior that cannot be duplicated through testing - mainly because it cannot be disproved, and yet it explains anything and everything.