Sending mail doesn't work from v0.7.1

[lunny]

Description

From go-gitea/gitea#35794.

Take a look at v0.7.0...v0.7.1 , It seems

-if useFullAddr {
-		return from[0].String(), nil
+
+	addr := from[0]
+	if !useFullAddr {
+		addr.Name = ""
	}
-	return from[0].Address, nil
+	return addr.String(), nil

The problem maybe caused by
addr.Name = "" && addr.String() is not equal to addr.Address.

failed to issue MAIL command: 555 5.5.2 Syntax error, cannot decode response. For more information, go to 5.5.2 https://support.google.com/a/answer/3221692 and review RFC 5321 5.5.2 specifications. 4fb4d7f45d1cf-64068f74a56sm1990428a12.15 - gsmtp

To Reproduce

Using v0.7.0 version as dependency of Gitea, sending test email from admin ui. It works.
Using v0.7.1 or v0.7.2 version as dependency of Gitea, sending test email from admin ui. It doesn't work.

Expected behaviour

It should work like before.

Screenshots

No response

Attempted Fixes

No response

Additional context

No response

[wneessen]

Hi @lunny,

thanks for flagging this, I'll have to get a gitea instance set up to do some testing, so please bear with me a day or two.

[wneessen]

Hi @lunny,

I took a look at the Gitea implementation and I was able to reproduce the issue. This is not a go-mail bug, though but an issue in how Gitea implements the mail client functionality. Gitea makes use of the low-level go-mail/smtp client instead of using go-mail's own Client. The Client of the smtp package is expecting some specific formatting that go-mail's Client will automatically satisfy.

The main issue is, that for the vulnerability fix that 0.7.1 and 0.7.2 introduced, the handling of the mail addresses was refactored. If you use the go-mail Client implementation this would be transparent to you. But since Gitea uses the smtp package directly, they need to adjust their code to adept this change. Previously the smtp Client would add the brackets <> around the mail from address when the Client.From() method was called. This changed in the 0.7.1 release. Due to this, when Gitea sets the mail from address, the SMTP client will send this to the mail server: MAIL FROM:your.address@example.com instead of the correct: MAIL FROM:<your.address@example.com>.

I was able to implement a very simple fix, in the Gitea code though. This might not be the ideal solution, but it works in my Gitea test installation and should give you an idea on how to address the issue. The better solution would probably be to use the go-mail Client instead, as this will make sure when the smtp package is updated, that the underlying functions are also updated and will work together.

The quick and dirty fix is this:

diff --git a/services/mailer/sender/smtp.go b/services/mailer/sender/smtp.go
index 8dc1b40b74..3207eee32f 100644
--- a/services/mailer/sender/smtp.go
+++ b/services/mailer/sender/smtp.go
@@ -128,7 +128,7 @@ func (s *SMTPSender) Send(from string, to []string, msg io.WriterTo) error {
                        return fmt.Errorf("failed to issue MAIL command: %w", err)
                }
        } else {
-               if err = client.Mail(from); err != nil {
+               if err = client.Mail(fmt.Sprintf("<%s>", from)); err != nil {
                        return fmt.Errorf("failed to issue MAIL command: %w", err)
                }
        }

I'll close this issue for now, since this is a Gitea implementation issue, not a go-mail bug, but please feel free to re-open if you find any other issue.

[silverwind]

Maybe go-mail/smtp should be moved to go-mail/internal/smtp if it's not meant to be consumed directly. It would have avoided the issue in first place.

[wneessen]

Maybe go-mail/smtp should be moved to go-mail/internal/smtp if it's not meant to be consumed directly. It would have avoided the issue in first place.

The smtp package can be consumed directly, it's just very low-level. I will make sure, that in future releases a possible breaking change in the smtp package is explicitly marked though, so that people that rely on the package can see it in the release notes.