Is there a way to disable certificate checks in Duplicacy’s email feature?
I don’t think that possible.
Here are other options of handling this: WebDav with self signed certificate can't connect
Are you referring to the web gui? I wasn’t aware that it would fail on self-signed certificate when sending emails.
@TheBestPessimist Thank, saw that. It’s not a great solution once you have several clients. 
@gchen Yeah, it’s about the web GUI. It pops up an error that the certificate could not be verified, which is technically correct. It’d be great if there was an option to skip that check.