How to set a generally accepted avatar for mail?

Question

gmail

Most mail systems now have an avatar of the sender of the letter, most often it has a stub avatar, but sometimes there is a client avatar.
I use Zoho for corporate mail, I put avatars there, but it comes with a stub to gmail.
SPF/DKIM - indicated

Answer 1

In mail protocols (SMTP/POP/IMAP, etc.) there is no concept of an avatar, so mail systems do not understand the "generally accepted avatar", there is simply no such thing. The avatar is interpreted by email clients by selecting it from the contact database. And since there is no worldwide database of contacts, there are no "generally accepted avatars" either (at least for now).