Problem with mail account sign in from google. Copy this domain's SSL certificate as the default for the chosen service cannot save

I have enable the "Send mail as:" option for some clients in order to be able send mail from their domain through gmail. I had some complains that they got error message while they to use this function. The message they get is

From Mail Delivery Subsystem

The response was: TLS Negotiation failed, the certificate doesn't match the host.

Strange thing is that when i go to Virtual Panel and press the buttons in order to copy domain's SSL certificate as the default for the chosen service (attached photo) problem get solved but only for some hours. When the problem returns i check again Virtualmin and buttons appear again and i have to click again in order to solve the problem. It seem that system cannot keep these settings but i cannot figure why :-/

Any help will be appreciated.

Thank you

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Comments

Also another issue that is strange is that despite all buttons after click disappear the button copy to Dovecot stays there. This is not necessary a problem but just asking.

Do your domains have their own private IP addresses? That would be needed to setup a private SSL cert that is used for SMTP for just that domain.

I am not sure if i understood what do you mean. No i don't think that have their own private ip. I don't know how to setup this. All domains have my server's ip address . Same setup i had while using cpanel. What is your recommendation?

Thank you for supporting me

I might be looking at the wrong problem then - Can you post the full contents, including headers, of the email in which you saw that "The response was: TLS Negotiation failed, the certificate doesn't match the host." error?

This is not an email. I am trying to set up gmail to send mail as one of my addresses. If i select port 25 and unsecured there in no problem. When i select ssl port 465 i receive the following message

Authentication failed. Please check your username/password.
Server returned an error: "TLS Negotiation failed, the certificate doesn't match the host., code: 0"

If i click buttons at the attached photo for the selected domain problem temporary get solved.

But now i notice that when i click buttons for one virtual host then the other virtual host i set up before has again buttons available so i think that your previous answer has a point.

But i don't' know what do you mean if every domain has it's own ip address, how can i setup this? Sorry if i don't explain very well