i did some work on this a while ago Tutorial - Testing Mail Protocols with SSL/TLS
the key thing to understand is what protocols you are trying to use where (which is what i am not sure)
but I've been having trouble with my email server and gmail.
I don't understand this. Are you using gmail to forward emails to your SMTP server?
If so here are the checks to run
openssl s_client -connect mail.jvond.com:25 -starttls smtp -tls1_2
openssl s_client -connect mail.jvond.com:587 -tls1_2
openssl s_client -connect mail.jvond.com:587 -starttls smtp -tls1_2
openssl s_client -connect mail.jvond.com:465 -tls1_2
As pointed out before none of these servers are currently creating an SSL connection.
SMTP has had many revisions which is why you need to be careful which port you use
I think google would prefer port 465 to be open which is SMTP with SSL by default.