How can I protect myself from sending spam emails by spoofing my mailboxes?

Question

Email

Good afternoon.
Essence: there is a domain moydomen.ru.
This week someone started sending emails allegedly from my mailboxes [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] and send out on topics that are in no way related to my sites - something about lottery tickets. I receive complaints from clients and letters to spam about non-delivery at [email protected] After opening the non-delivery letter and looking at the logs, I found the bounce.estismail.com server. I contacted estismail.com support. They wrote that this mailing was made using a spam program and they do not know how to protect against it.

I have two questions: how does such a mailing list harm my site moidomen.ru and my mailboxes?
And second: how to protect yourself from such mailings?

Answer 1

You must configure a strict DMARC policy and DMARC filtering.
https://habr.com/en/company/mailru/blog/315778/
DMARC requires SPF and DKIM. By themselves, SPF and DKIM will not help protect against fake emails.

Answer 2

Unfortunately, the target audience of these letters will never see the difference of whether these letters are from you or not. Therefore, they can undoubtedly do some damage to the reputation.
Either not react here, or do it as quickly as possible) Again, somehow inform your audience that an attack is possible.

Answer 3

Set up spf and dkim, it will be enough for such letters on "decent" mail servers to fall into at least spam, and perhaps not be accepted at all.
In case of complaints from your customers, encourage them to use these technologies.

Answer 4

How does such mailing harm my site moidomen.ru and my mailboxes?

reputational costs, getting into spam lists by domain name

How to protect yourself from such mailings?

no way. Of course, you can adjust SPF/DKIM - this will increase the permeability of normal emails and reduce the permeability of spam ones - but not everywhere.

Answer 5

I "scored" in due time on this problem, but no complaints were written to me.
Complained to hosters and domain owners... to no avail.
A normal mailer always checks the reverse zone of the bounce.estismail.com server that sends letters from moydomain.ru and the letters will be discarded.
If there is nothing to do:
1) They wrote to you about SPF/DKIM
2) Check the source code of the letters that your IP addresses and domain names are not there. Suddenly all the same backdoor in your network.
3) go to https://www.estismail.com/price and you will understand that they are useless to write... probably.
4) Ask a question on this site: How to add a domain to the list https://www.dnsbl.info/ )))