How to set up an auto-responder for a letter?

Question

Marketing

Good afternoon.
For several days I have been conjuring over how to make an autoresponder mail.
It is necessary that when a new letter arrives on the box, an auto-reply to this letter with an attached file will work.
What I did:
1. Yandex is not suitable, because there is no way to customize the letter template and attach a file
2. Gmail - it does not work stably, sometimes it sends letters, sometimes it doesn't. And sends to one more recipient every 4 days. - didn't work either
3. I set it up in the ISP panel, you can attach a file, you can't customize the template. But it works very unstable, besides, the IP of my VDS is not the fact that it is clean and letters are often sent to spam.
Please help me find a way to solve this problem. Preferably simple and understandable.

Answer 1

Alexander, good afternoon!
In response to which user action should the email be sent? If after filling out the form on the site, then "fasten" the subscription form of the mailing service. And already in it, set up an automatic letter in the design you need.
Only the file will not need to be physically attached to the letter, but to give a link to it.