"Enable SMTP SSL" on Server Settings

[james7342]

I think I may have stumbled across an issue though I thought I would start it as a discussion first. I currently use PowerDNN/Managed.com SMTP Relay service for sending messages. Installed HotCakesModule and noticed an error when it was sending emails. Worked with Will Strohl on it and I think may have found an issue.

HotcakesCommerce/hotcakes-commerce-core#453

I'm not convinced that the "Enable SMTP SSL" is actually working properly or at least enforcing SSL. Managed.com confirmed their SMTP relay doesn't support SSL, but with this option checked I can still send mail without issue. Does DNN try SSL first then fallback to non SSL if it fails? The only module that is having an issue is HCC. All of the other DNN emails work regardless if this option is toggled on/off.

[bdukes]

The MailKit provider does not do anything with the Enable SMTP SSL configuration option. Instead, it uses an "auto" setting within MailKit, which detects the correct mode based on the port. I believe we needed to do this to support STARTTLS automatically (at least, without then also exposing other configuration that the older mail provider couldn't support).

Dnn.Platform/DNN Platform/Library/Services/Mail/MailKitMailProvider.cs

Line 43 in 90e6ac4

smtpClient.Connect(host, port, SecureSocketOptions.Auto);

[bdukes]

According to https://stackoverflow.com/a/57008444/2688:

MailKit treats port 587 the same as it treats 25. In other words, it treats port 25 and 587 as a plain-text connection port but will switch to SSL/TLS if requested to do so via STARTTLS.

I agree that a note would be helpful.

[james7342]

That explains what I'm seeing and why my configuration/testing is successful.

Better yet on the enhancement- Check if MailKit is being used and disable the "Enable SMTP SSL" option and cover the reason in the information popup. :-)

[james7342]

@bdukes do you want me to open a issue for an enhancement and link this discussion?

[bdukes]

I just submitted #5756 to add a note

[james7342]

Thank you..