Can Subject Alternative Name accommodate multiple virtual mail domains?

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http://serverfault.com – I am currently running a postfix server with self signed certificates serving one mail domain, mycompany.com, the mail server is mail.mycompany.com and so is the CN of the certificate. Now, I need to add a new domain to it. The new domain name is mycompany.net to the same server. Since the users already have the root of the old certificate, I'd like to reuse that. However, I'd like to issue a new certificate so users using the SMTP from Outlook/Thunderbird of mail.mycompany.net do not get warnings. If I understand correctly, if I issue a new certificate with CN=mail.mycompany.com and a subje (HowTos)