@helebor wrote: DavidC, I appreciate your efforts to troubleshoot from ground zero up - thanks.  I think i need to keep searching for some way ro install a CA certificate on this PC.  If I find a solution, I will report back. David, sorry for misspelling your moniker...I have solved the problem by giving up on it an upgrading to the latest version of The Bat! emai; client software. Whatever it was, it has now been corrected by ditching that old version.  Thanks for your efforts. ... View more

@david64 wrote: @helebor . Considering the recipients that get this error message, are they on one domain or multiple domains? Do they have trouble receiving emails from other senders? If any failing recipients are gmail or hotmail addresses, you could make your own account there for testing. I'm assuming it is you using The Bat client. Do you know how the failing recipients access their email? Browser or mail client?   DavidC, I appreciate your efforts to troubleshoot from ground zero up - thanks.  I think i need to keep searching for some way ro install a CA certificate on this PC.  If I find a solution, I will report back. ... View more

@david64 wrote: @helebor . Certificate errors normally occur between a client and the mail server. When that happens, no emails are sent or received. --- It appears that the error occurs only for some recipients, upon their fetching mail.   Considering your emails that aren't sent, is there a specific domain that fails or multiple domains? ----- Further to the previous para, the emails are *sent* in all cases:  the blockage occurs at the recipinet mail server (or somewhere in the intermediate chain).   Are the failures consistent? A particular recipient will either always work or always fail? ---- I think so, proabably.   From reading the product help, it seems like the client can encrypt the data part of emails using a key specific for each contact address, or, optionally, not encrypt. And, the recipient must have a matching key to decrypt. ----- Not relevant here.   Might be easier to ask The Bat! support about the error message. It shouldn't matter that your version might be unsupported. The error message has a more detailed meaning in relation to "address book". ------ ...except that they do not support *any* problem if the version is not current.   Thanks, though.   ... View more

You tell me...! ;-) ... View more

"Unknown CA certificate. The server didn't provide a root certificate and there is no corresponding root certificate in your address book." Client isThe Bat! Home Edition Version 7.4.4 (64-bit). (Yes, I know it's old!)  The thing is, I haven't encountered this problem before and I don't really know where to start looking. ... View more