olemus
(2a) kasutajanimi meiliserveri poole pöördumiseks
= username for accessing the email server

(2b) meiliaadressi vasakus pooles kasutatav nimi
= email sender name used in the left part of email address

ülevaateid
https://www.hostingclues.com/professional-email-id/

https://neverbounce.com/blog/format-email-address

https://blog.cloudhq.net/how-to-choose-a-good-email-name-in-2022/