Change SMTP to enable sending message to a gmail address

[sophiege]

Hello,
I have two addresses on Thunderbird, from two different Internet service provider, hence two different SMTPs.
I can use the same SMTP for both addresses to send email, except for gmail addresses, where I have to change SMTP, using the one corresponding to the sending address, to be able to send message to a gmail address.
If I don't do that, my message is rejected for security reasons ("This message does not pass authentication checks").
For security, one SMTP is STARTTLS the other is SSL/TLS.
Is there a way to avoid this SMTP change only for this kind of addresses?
Thanks
S

[DanRaisch]

It's not clear why you don't just leave the settings in the way that works for messages going to Gmail. What's the problem with using two SMTP server?