Where can I find a mailing list service with an internal mailbox?

Question

Email

Given: a script that generates a letter.
Task: send this letter to a third-party service for subsequent distribution to subscribers. This implies that such a service must have its own mailbox for receiving letters. For such purposes, the Listbox.com service was previously found, which assigns an ID to each of its clients (it is also a valid postal address). However, now for certain reasons we cannot work with them.
The reason for the trouble: the script that generates the letter is written in such a way that all attachments added to letters (meaning pictures) are displayed in any mail clients without a request to download external content.
Need a service that can provide receptionour letter to your server for subsequent forwarding . Standard service templates are not acceptable. Your suggestions.

Answer 1

sendgrid