server B produces an error

{
  "ts": 1663009665363,
  "type": "deferred",
  "direction": "outbound",
  "uuid": "B17FA8D4-5997-4FE6-8636-400140195457.1",
  "messageId": null,
  "mailFrom": "<>",
  "spamStatus": null,
  "rcptTo": [
    "<no-reply@serverB.com>"
  ],
  "message": "Tried all MXs",
  "delay": 8192
}

and server A produces the error

{
  "ts": 1663009909718,
  "type": "bounce",
  "direction": "outbound",
  "uuid": "380CB958-8DD9-45DC-B9C3-13F89C1FD866.1.1",
  "messageId": "<f993a729-8533-909f-f3d0-be386c19df96@draglabs.com>",
  "mailFrom": "<no-reply@draglabs.com>",
  "spamStatus": null,
  "rcptTo": [
    "<user@serverB.com>"
  ],
  "message": "Some recipients failed: <user@serverB.com>",
  "mx": {
    "priority": 0,
    "exchange": "127.0.0.1",
    "port": 2424,
    "using_lmtp": true,
    "family": "A",
    "bind_helo": "my.draglabs.com"
  },
  "bounced_rcpt": [
    {
      "original": "<user@serverB.com>",
      "original_host": "serverB.com",
      "host": "serverB.com",
      "user": "user",
      "reason": "550 5.1.1 <user@serverB.com> User doesn't exist: user@serverB.com",
      "dsn_action": "failed",
      "dsn_smtp_code": "550",
      "dsn_smtp_extc": "5.1.1",
      "dsn_status": "5.1.1",
      "dsn_smtp_response": "<user@serverB.com> User doesn't exist: user@serverB.com",
      "dsn_remote_mta": "127.0.0.1"
    }
  ]
}

What I think is happening is that because I enabled email on Server A, Server A is automatically looking for that user's email inbox to drop the email as opposed to routing it though the internet where is would use the MX records listed in the DNS.

So the question becomes how do you log into an email server without enabling inbound email.

Or how do you convince cloudron to be happy sending email from a different subdomain? like mail.serverb.com without setting the root of server be to my.mail.serverb.com

yes confirmed

I did some tests and they way it is configured now I can email anyone other than <user>@DomainB.com and if I disable "Incoming Email" then the server A user "relay@serverB.com" cannot authenticate for the purpose of sending emails.

@subven @girish - Any Ideas on a solution here?

• Add the domain of Cloudron server B into Cloudron server A.
• Disable mail from validation in Cloudron server A for the added domain.
• Create a "relay" user in Cloudron server A and also a relay@ mailbox.
• Set the above credentials as the external relay in Cloudron server B.

This will allow server B to send emails via server A for that specific domain you added. You have to repeat for every domain you want to relay.