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https://support.microsoft.com/ru-ru/topic/%D0%BF%D1%80%D0%BE%D1%82%D0%BE%D0%BA%D0%BE%D0%BB-%D0%BF%D1%80%D0%BE%D0%B2%D0%B5%D1%80%D0%BA%D0%B8-%D0%BF%D0%BE%D0%B4%D0%BB%D0%B8%D0%BD%D0%BD%D0%BE%D1%81%D1%82%D0%B8-kerberos-%D0%BD%D0%B0-%D0%BE%D1%81%D0%BD%D0%BE%D0%B2%D0%B5-gssapi-%D0%BD%D0%B5-%D0%BF%D1%80%D0%B5%D0%B4%D0%BB%D0%B0%D0%B3%D0%B0%D0%B5%D1%82%D1%81%D1%8F-%D0%BA%D0%BB%D0%B8%D0%B5%D0%BD%D1%82%D0%B0%D0%BC-imap-%D0%B2-exchange-server-2013-28583c63-db59-46db-023d-a6deac8ecb5d

https://docs.microsoft.com/en-us/exchange/mail-flow/connectors/proxy-outbound-mail?view=exchserver-2019

http://avt-lab.ru/thebee.htm