Allow sending mails without authentication

[kolaente]

Is your feature request related to a problem? Please describe.

There are users who run their smtp servers without authentication (for example in a private network). Currently, this package is unable to connect to such mail servers.

I've tried a few things and got different error messages as a result:

1. With auth type plain and no username/password:

dial failed: SMTP AUTH failed: 535 Incorrect authentication data

2. Without the mail.WithSMTPAuth option or uncommenting https://github.com/wneessen/go-mail/blob/main/client.go#L327-L329:

send failed: sending RCPT TO command failed: 550 relay not permitted

3. With an empty password and username.

None of these three things seem to work.

Related go-vikunja/vikunja#34 (comment)

Describe the solution you'd like

Ideally, there would be an option like mail.WithoutAuthentication which does not even try to authenticate and instead just sends the mail straight away. I thought this would work when removing lines https://github.com/wneessen/go-mail/blob/main/client.go#L327-L329 but it didn't.

Describe alternatives you've considered

No response

Additional context

No response

[wneessen]

Hi, thanks for the request.

This is actually a false-positive. When used without the mail.WithSMTPAuth option, the library in fact does send mails without any authentication - if the mail server allows this.

As you stated in 2. the 550 relay not permitted message means, that the mail server does not allow relaying mails - meaning sending mails without being either authenticated or being IP whitelisted. I just confirmed with my local Postfix installation, that I am able to send mails without prior authentication.

I suggest that you check the local mail server configuration to see if local relaying is allowed or not.
In Postfix you can accomplish this by

mynetworks = 127.0.0.0/8
smtpd_recipient_restrictions = permit_mynetworks [....]

[kolaente]

Thanks for the explanation! Looks like my lack of mail server knowledge is to blame here :)

I've checked the implementation and config again and it seems to work fine when I run everything on a server that's allowed to talk to the mail server.

[mitar]

I also got confused how to configure no-authentication SMTP. Luckily I found this issue.

[wneessen]

Gald this helped you. I'll consider adding a FAQ section to the go-mail website and adding this, as it seems a common issue.

[mitar]

Maybe easier is to define SMTPAuthType None which equals to an empty string. This is what I did in my own codebase now.

[wneessen]

Gotta evaluate that.