Add support for sSMTP revaliases configuration

[valentinocossar]

Hi,

I'm experiencing some issues with Mailgun and Gmail, some emails sent by a server configured with Mailgun as SMTP to a Gmail account have a non-compliant domain name as From header.

This is the Mailgun log.

{
    "severity": "permanent",
    "tags": [],
    "storage": {
        "url": "https://sw.api.mailgun.net/v3/domains/example.com/messages/key_value",
        "key": "key_value"
    },
    "delivery-status": {
        "tls": true,
        "mx-host": "aspmx.l.google.com",
        "code": 550,
        "description": "",
        "session-seconds": 0.23837614059448242,
        "utf8": true,
        "attempt-no": 1,
        "message": "5.7.1 Our system has detected that this message is\n5.7.1 not RFC 5322 compliant:\n5.7.1 'From' header has non compliant domain name.\n5.7.1 To reduce the amount of spam sent to Gmail, this message has been\n5.7.1 blocked. Please visit\n5.7.1  https://support.google.com/mail/?p=RfcMessageNonCompliant\n5.7.1 and review RFC 5322 specifications for more information. q63si546488qki.5 - gsmtp",
        "certificate-verified": true
    },
    "recipient-domain": "example.com",
    "id": "id_value",
    "campaigns": [],
    "reason": "generic",
    "user-variables": {},
    "flags": {
        "is-routed": false,
        "is-authenticated": true,
        "is-system-test": false,
        "is-test-mode": false
    },
    "log-level": "error",
    "timestamp": 1519779343.260742,
    "envelope": {
        "transport": "smtp",
        "sender": "fail2ban@example.com",
        "sending-ip": "1.2.3.4",
        "targets": "info@example.com"
    },
    "message": {
        "headers": {
            "to": "info@example.com",
            "message-id": "id_value@example.com",
            "from": "Fail2Ban <fail2ban>",
            "subject": "[Fail2Ban] sshd: started on VPS"
        },
        "attachments": [],
        "size": 526
    },
    "recipient": "info@example.com",
    "event": "failed"
}

Seems this is happening due to the FromLineOverride='Yes' set by default in the Trellis sSMTP configuration.

To fix this issue I have two options:

1. Find every service on the server that could send an email and edit manually the configuration of the sender.
2. Change the value FromLineOverride to No. But changing this parameter causes the emails sent by the server to have a From header dependent to the user who sends the email (e.g. web@examaple.com). However, there's a sSMTP option to map every user to a custom From address using the aliases in the /etc/ssmtp/revaliases.

This pull request introduces the feature to customize the /etc/ssmtp/revaliases during provision in the sSMTP configuration task.

The feature is disabled by default because FromLineOverride it's enabled by default.

This is my personal use case to solve an issue, but I think that this feature could be useful to all people that want to have a complete control on the sSMTP configuration using Trellis.

Thank you.

[swalkinshaw]

🤔 interesting.

This makes sense I think. FromLineOverride=Yes allows WordPress to easily set the From header which we'd want. But as you said, anything else on the server that sends email without explicitly setting the From will get a default like "Fail2Ban <fail2ban>" which isn't valid.

I'm wondering if there's a better default though. What if we left FromLineOverride=Yes and set these default aliases?

[valentinocossar]

I did a lot of test with sSMTP and found that if I left FromLineOverride=Yes the result would be dependent on which command the program uses to send the email.

Here my /etc/ssmtp/revaliases file:

root:test@test@example.com:smtp.mailgun.org:587
admin:test@test@example.com:smtp.mailgun.org:587

Here are some tests:

1. Sent via mail with specified From:
   Command: echo "This is the message body" | mail -s "This is the subject" info@example.com -aFrom:noreply@example.com
   Result: From:noreply@example.com
2. Sent via mail with non-specified From:
   Command: echo "This is the message body" | mail -s "This is the subject" info@example.com
   Result: From:admin@hostname, where the hostname is the same I have in the /etc/mailname file
3. Sent via ssmtp with specified From:
   Command: echo "From:noreply@example.com" | ssmtp info@example.com
   Result: noreply@example.com
4. Sent via ssmtp with non-specified From:
   Command: echo "Subject:Test" | ssmtp info@example.com
   Result: From:test@example.com, same as reported in the /etc/ssmtp/revaliases file
5. Via sendmail the results are the same as the ssmtp because sendmail is a symlink of ssmtp.

If the service doesn't provide the From header and the mta is ssmtp or sendmail, the /etc/ssmtp/revaliases file works as expected, but the problems come out when the service overwrites the From header with a non-compliant custom one.

Maybe changing the sender for Fail2Ban in some way could solve the problem but it's not a solution because it's not the only service that sends email from the server. That's why I specified that one of the solutions for the problem is to change the From for every service that sends emails, but I don't think it's easy. In fact, I've got other emails with the same problem reported in the log above but from other services that are not Fail2Ban.

In my opinion, this solution is more generic, it's not only to solve this specific problem but it's a more complete control over the sSMTP configuration if anyone needs it.

[pySilver]

I've had this issue some time ago and beside using revalises I've added

- name: ssmtp configure default sending domain
  template:
    src: mailname.j2
    dest: /etc/mailname

with

# mailname.jd file:
{{ mail_hostname }}

[valentinocossar]

Hi @pySilver, thank you for the feedback, I already have /etc/mailname on my server with the default domain set by OVH and it's a valid domain name (vps112233.ovh.net) but this is not resolving the issue for me. The From header is overwritten by Fail2Ban (or other services) every time that sends an email and when it's not overwritten by a service the server sends the email with the default domain seen above.

[valentinocossar]

@swalkinshaw at the end, what you think about the implementation of this feature? 🙂

[swalkinshaw]

Thanks @valentinocossar

[valentinocossar]

Thank you @swalkinshaw!