O seu problema é que você não configurou mecanismos anti-spoofing para o seu servidor de e-mail. No século XX, costumava enviar e-mails de: [email protected] sem problemas.
1) Ative, pelo menos, a verificação de registros PTR de hosts de conexão no Lotus Domino: link
Verify connecting hostname in DNS:
Enable the following fields in the Configuration Document --> Router/SMTP tab --> Restrictions and Controls --> SMTP inbound controls:
Choose one: 1. Enabled - Domino verifies the name of the connecting host by performing a reverse DNS lookup. Domino checks DNS for a PTR record that matches the IP address of the connecting host to a host name. If Domino cannot determine the name of the remote host, because DNS is not available or no PTR record exists, it does not allow the host to transfer mail. Although Domino accepts the initial connection, later in the SMTP transaction, it returns an error to the connecting host in response to the MAIL FROM command.
NOTE: Internet SMTP hosts are not required to have PTR entries in DNS. As a result, when this field is enabled, the SMTP task may reject connections from valid SMTP hosts.
- Disabled - (default) Domino does not check DNS to verify the name of the connecting host.
2) Verifique os registros PTR, SPF, DKIM e DMARC do seu domínio link
Esses registros são armazenados no servidor DNS e, portanto, devem ser configurados pelo seu ISP, mas geralmente fornecem alguma interface para permitir que os usuários editem seus próprios registros DNS.
Você deve verificar o estado de seus registros DNS usando: link
Você deve definir o SPF para especificar que é o seu servidor de e-mail que está autorizado a enviar e-mails do seu domínio e nada mais.
Let's look at an example to give you an idea of how SPF works. Bob owns the domain example.net. He also sometimes sends mail through his GMail account and contacted GMail's support to identify the correct SPF record for GMail. Since he often receives bounces about messages he didn't send, he decides to publish an SPF record in order to reduce the abuse of his domain in e-mail envelopes:
example.net. TXT "v=spf1 mx a:pluto.example.net include:aspmx.googlemail.com -all"
The parts of the SPF record mean the following: v=spf1 SPF version 1 mx the incoming mail servers (MXes) of the domain are authorized to also send mail for example.net a:pluto.example.net the machine pluto.example.net is authorized, too include:aspmx.googlemail.com everything considered legitimate by gmail.com is legitimate for example.net, too -all all other machines are not authorized
This example demonstrates but a small part of SPF's expressiveness. Do not take it as a guideline for building your own record — things might not work out as you expect and legitimate messages might get blocked! Instead, learn more about the record syntax, or get the complete picture by studying the full specification. Community support is available.