> SMTP "с обвязкой"

Там очень забавная обвязка когда нужна какая-то хоть на словах безопасность хоть чего-то.

> Вам же сказали - SMTP "с обвязкой" за день-два

RFC 5321 — Simple Mail Transfer Protocol. This is a protocol used to send emails between computers.

RFC 5322 — Internet Message Format (basic format of an email message), previously RFC 822 and RFC 2822.

RFC 5228 — Sieve: An Email Filtering Language. Sieve is a language used to file, filter, and forward emails

RFC 3207 — SMTP Service Extension for Secure SMTP over Transport Layer Security. This is a protocol used to upgrade a plaintext SMTP connection to an SSL/TLS encrypted one.

RFC 6376 — DomainKeys Identified Mail (DKIM) Signatures. This allows emails to be signed by a particular domain to ensure they haven't been tampered with, and to say that that domain claims responsibility for the message.

RFC 8617 — Authenticated Received Chain (ARC). This is a protocol to provide an authenticated chain of custody for messages that have passed through intermediate mail servers, such as through forwarding.

RFC 2045 — Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies. This is an extension to the email message format to support attachments and non-ASCII data in emails.

RFC 2046 — Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types.

RFC 2047 — MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text.

RFC 2231 — MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations.