Using CID to reference attached images in html mails

[kolaente]

Hey there, really nice library, coming from gomail.

I've been trying to embed an image in a mail and referencing it via cid: but couldn't really get it to work.

Basically, I want to do this: https://stackoverflow.com/a/41994121/10924593

I've managed to add the file to the mail as an attachment but using cid:filename.png to actually reference the image does not seem to work.
I think I'd need to set an extra attachment header to set the content id? Or something like that?

[kolaente]

Okay looks like this just works™ when I use EmbedReader instead of manually adding the file as an attachment.

[wneessen]

Maybe as an additional side note on why this happens...

The Embed-methods add a inline tag to the Content-Disposition header, as well as a Content-Id: <file.xxx> header to the attached file headers. The Content-ID header is what is referred to when using the CID tag.

[kolaente]

Awesome, thanks for the explanation.

You don't have to use the EmbedReader btw. You can also use Msg.EmbedFile() directly.

I know, but using the Reader allows me to embed the file with go:embed. Or can I do that with EmbedFile as well?

[wneessen]

No, you are correct. At the moment. for go:embed the EmbedReader() is the right solution. I might add a EmbedFile version that supports embed.FS in one of the next releases.

[wneessen]

With the latest release: https://github.com/wneessen/go-mail/releases/tag/v0.2.5 you can now embed files from embed.FS directly without having to use EmbedReader()

[kolaente]

Works perfectly! Thanks a lot!