Thanks Joe, I trust your gut with this stuff - you have a little bit of experience with Virtualmin 
So, I have a ‘send as’ email address set up in Gmail that has been working fine, but now when I try to send, I get a “The settings for your ‘Send mail as’ account are misconfigured or out of date” error email from Gmail.
I deleted and reset the ‘send as’ account up from scratch (a potential solution from another forum).
That works, but only if I use the unsecured connection option. I used to have it set to tls.
Now, when I try to use tls, I’m getting an error that says:
"Server returned error: “TLS Negotiation failed, the certificate doesn’t match the host., code: 550”
Ugh. I checked and my let’s encrypt cert is active and includes the mail server domain.
I wondered if regenerating the let’s encrypt cert would help, but I get an error when I try to do that:
### Failed to request certificate : Missing file to read at virtual_server::/usr/libexec/webmin/virtual-server/feature-dns.pl line 3484
I’m not sure if that’s related to the email problem I’m having. Probably not.
I tested the tls for the domain on TLS Checker - Instant Results | CDN77.com and it says TLS 1.2 is enabled, TLS 1.3 is disabled.
Not sure what to do next. The ‘send as’ works if I have the setting at ‘unsecured’, but I have this set up for someone else who is in private practice, it would be nicer if it was secured,
Chris