How to correctly set up Postfix and Dovecot on two domains?

Question

Debian

Set up a mail server. Everything worked fine until we had to attach another domain. After that, the mail itself seems to work (sending and receiving), but not all mail clients connect to it. The problem, I believe, is in SSL certificates (it is impossible to hang a separate SSL certificate for each domain).
I did all the mail server setup using this link.
Here is the error log:

Apr 11 18:22:09 multigramen postfix/smtpd[1442]: warning: cannot get RSA certificate from file "/etc/ssl/domain.ru.public.pem": disabling TLS support
Apr 11 18:22:09 multigramen postfix/smtpd[1442]: warning: TLS library problem: error:02001002:system library:fopen:No such file or directory:../crypto/bio/bss_file.c:288:fopen('/etc/ssl/domain.ru.public.pem','r'):
Apr 11 18:22:09 multigramen postfix/smtpd[1442]: warning: TLS library problem: error:20074002:BIO routines:file_ctrl:system lib:../crypto/bio/bss_file.c:290:
Apr 11 18:22:09 multigramen postfix/smtpd[1442]: warning: TLS library problem: error:140DC002:SSL routines:use_certificate_chain_file:system lib:../ssl/ssl_rsa.c:615:
Apr 11 18:22:10 multigramen postfix/smtpd[1442]: connect from unknown[IP-address]
Apr 11 18:22:10 multigramen postfix/smtpd[1442]: disconnect from unknown[IP-address] ehlo=1 auth=0/1 quit=1 commands=2/3
Apr 11 18:23:03 multigramen dovecot: imap-login: Login: user=<E-Mail>, method=PLAIN, rip=IP-address, lip=IP-address, mpid=1460, TLS, session=<NrEWbQWj42e5HrE6>
Apr 11 18:23:04 multigramen dovecot: imap(E-Mail)<1460><NrEWbQWj42e5HrE6>: Logged out in=96 out=641 deleted=0 expunged=0 trashed=0 hdr_count=0 hdr_bytes=0 body_count=0 body_bytes=0
Apr 11 18:24:32 multigramen postfix/submission/smtpd[1490]: connect from unknown[IP-address]
Apr 11 18:24:36 multigramen postfix/submission/smtpd[1490]: disconnect from unknown[IP-address] ehlo=1 auth=0/1 rset=0/1 quit=1 commands=2/4

Does anyone have any ideas? I apologize if this question seems stupid for someone, this is the first time I have encountered this and I have not been able to solve this problem for a long time.

Answer 1

Dovecot:
https://wiki.dovecot.org/SSL/DovecotConfiguration#...

local_name imap.example.org {
ssl_cert = /ssl/certs/imap.example.org.crt
ssl_key = /ssl/private/imap.example.org.key
}
local_name imap.example2.org {
ssl_cert = /ssl/certs/ imap.example2.org.crt
ssl_key = /ssl/private/imap.example2.org.key
}
# ..etc..