How to set up Dovecot to transfer mailboxes to Yandex?

Question

Yandex

Hello.
I want to transfer corporate mail from a local server (which I did not set up) to postfix + dovecot on Yandex.Connect.
For testing, I started one mailbox there and tried to import mail, but the attempt ends with an error. Surely the problem is that postfix does not allow anyone to download mail.
How to resolve this matter? Here is the server log at the time of the attempt to import the mailbox from Yandex:

Aug 10 20:37:18 bserv postfix/smtpd[23228]: lost connection after CONNECT from unknown[103.44.50.114]
Aug 10 20:37:18 bserv postfix/smtpd[23228]: disconnect from unknown[103.44.50.114]
Aug 10 20:37:18 bserv postfix/smtpd[23244]: connect from unknown[185.32.63.21]
Aug 10 20:37:18 bserv postfix/smtpd[23244]: NOQUEUE: reject: CONNECT from unknown[185.32.63.21]: 450 4.7.1 Client host rejected: cannot find your hostname, [185.32.63.21]; proto=SMTP
Aug 10 20:37:18 bserv postfix/smtpd[23244]: lost connection after CONNECT from unknown[185.32.63.21]
Aug 10 20:37:18 bserv postfix/smtpd[23244]: disconnect from unknown[185.32.63.21]
Aug 10 20:37:18 bserv postfix/smtpd[23243]: lost connection after CONNECT from unknown[194.44.246.83]
Aug 10 20:37:18 bserv postfix/smtpd[23243]: disconnect from unknown[194.44.246.83]
Aug 10 20:37:19 bserv postfix/smtpd[23228]: warning: 91.98.101.44: hostname 91.98.101.44.pol.ir verification failed: Name or service not known
Aug 10 20:37:19 bserv postfix/smtpd[23228]: connect from unknown[91.98.101.44]
Aug 10 20:37:19 bserv postfix/smtpd[23228]: NOQUEUE: reject: CONNECT from unknown[91.98.101.44]: 450 4.7.1 Client host rejected: cannot find your hostname, [91.98.101.44]; proto=SMTP
Aug 10 20:37:19 bserv postfix/smtpd[23228]: lost connection after CONNECT from unknown[91.98.101.44]
Aug 10 20:37:19 bserv postfix/smtpd[23228]: disconnect from unknown[91.98.101.44]
Aug 10 20:37:44 bserv postfix/smtpd[23243]: warning: 159.224.194.220: hostname 220.194.224.159.triolan.net verification failed: Name or service not known
Aug 10 20:37:44 bserv postfix/smtpd[23243]: connect from unknown[159.224.194.220]
Aug 10 20:37:44 bserv postfix/smtpd[23243]: NOQUEUE: reject: CONNECT from unknown[159.224.194.220]: 450 4.7.1 Client host rejected: cannot find your hostname, [159.224.194.220]; proto=SMTP
Aug 10 20:37:46 bserv postfix/smtpd[23243]: lost connection after CONNECT from unknown[159.224.194.220]
Aug 10 20:37:46 bserv postfix/smtpd[23243]: disconnect from unknown[159.224.194.220]
Aug 10 20:39:10 bserv postfix/smtpd[23243]: warning: 89.43.78.222: address not listed for hostname hostmaster.netbudur.com
Aug 10 20:39:10 bserv postfix/smtpd[23243]: connect from unknown[89.43.78.222]
Aug 10 20:39:10 bserv postfix/smtpd[23243]: NOQUEUE: reject: CONNECT from unknown[89.43.78.222]: 450 4.7.1 Client host rejected: cannot find your hostname, [89.43.78.222]; proto=SMTP
Aug 10 20:39:10 bserv postfix/smtpd[23243]: lost connection after CONNECT from unknown[89.43.78.222]
Aug 10 20:39:10 bserv postfix/smtpd[23243]: disconnect from unknown[89.43.78.222]