Mail Not Remembering to Trust Certificate for SMTP Server

I deleted the old certificate (expired) from Keychain and Mail saved the new one, but it is still not working. If I double-click on the certificate I see that the 'Use Custom Settings' option is selected (see the attached screenshot). However, if I change this setting to 'Always Trust', it will not be saved, so when I double-click on the certificate again, the 'Use Custom Setting' is again selected.

What is happening? Please help!

Fantastic news! It seems that Apple fixed the Mail issue in macOS 10.12.4. 🙂

When I tried to send an e-mail in Mail on macOS 10.12.4, Mail asked again whether to trust the certificate. I selected 'Always Trust' and then, unlike never before, it prompted me for my administrator password. After this, it just works now. I closed and reopened Mail, and even restarted the computer and I've got no more certificate error, and Mail sends messages as it should.

Hopefully they've fixed the other bugs in Mail, like the frequent crashes, as well as in Preview.

Life is good now...

No, it still does not work. When I open Keychain I can only see a certificate that expired on 26 May 2014. The new certificate that Mail displays would expire on 3 May 2020. But even if I select 'Always Trust' in Mail when accepting the certificate, it does not get copied over to Keychain.

Why is the new certificate not being copied over to Keychain? Anyone, please?

Unfortunately, none of your suggestions worked, but thank you, anyway.

As I mentioned in my post above, if I change the first setting to 'Always Trust', it will not be saved. When I check the 'Get Info' again, the certificate reverts to 'Use Custom Settings'.

What needs to be done such that the system saves and remembers the 'Always Trust' option? Thanks.

I wish I knew what was going on with Mail. I tend to think it may be an Apple Mail bug. I double-checked with the e-mail provider and all IMAP/SMTP parameters I am using are correct. Also, everything works perfectly well with the same parameters on my iPhone and iPad, and these never ask me about invalid certificates.

The even more frustrating issue is that Mail keeps crashing on me very, very often, which was not happening before Sierra. Every time Mail stops responding I have to kill it and restart it, and hence go through the same invalid certificate procedure/hassle over and over again.

Thirdly, having several e-mail accounts in Mail, the program seems to be taking the liberty of changing the outgoing server at its own will. Even though I had the correct account selected, e-mails that I sent went out from the wrong addresses. Very embarrassing!

Adding to this the frustration that Preview shows mark-ups in PDF files only randomly - so I was embarrassed when I told a client from work that his PDF document had no mark-ups when it actually had - plus from a tonne of other weird issues in Sierra, and I am beginning to question the stability of macOS and whether perhaps it may be time to switch to other platforms.

I my Keychain I can see a single certificate for the SMTP server under 'Certificates' but it expired on 26 May 2014. Mail did not save the the new certificate here.

HELP! Anyone please?

HELP, anyone? Please!