Same problem as the linked threads, i.e. a private message (PM) stating the account's electronic mail address is invalid; however, the address is valid (account has been in existence for a long time & no change was made to the address) - and unique. Is it possible the policy was changed - and, in the process, domain owners who use unique addresses were overlooked (e.g. 'email@example.com' went from being valid to invalid because the domain's name is part of the address)? If not, perhaps a transient problem resulted in the address being aggressively marked invalid (i.e. marked invalid on the first failed attempt)?
The last message received from the forum (a monthly newsletter) was 'Wed, Nov 5, 2014 at 2:19 AM'; the notice regarding the address was received '11/6/2014 9:49:41 PM'. Of course, no mail to the address/from the forum after that...
PS: Thanks in advance for any time & attention afforded to the same...
Also, just wanted to pass along a compliment about the forum; having never seen a BBS that automatically selects threads that are similar to a given posting (as evident from the post referencing two threads & being submitted as such) the discovery of the same was a neat surprise - thank you!
(Adding a thread in response to the dialog will have to wait until the next attempt - as a search turned up 'https://coderanch.com/t/525473' in response to "invalid email address"... but said thread doesn't have the word "invalid" and doesn't appear to be of a form accepted by the system...)