After some more troubleshooting I found the problem was with protonmail.
In gmail the attached file shows up, no problem.
In protonmail the attached file doesn't show up.

cool, thanks for finding that out

if someone wants to dig into this we could maybe find a way that supports both gmail and protonmail

Interestingly there's some other stuff I found.
If I send it to my gmail, using the script, there's no issue.
If I forward that email from my gmail to protonmail, there's no issue.

I've also got automatic forwarding set up from my gmail to protonmail.
The email that was automatically forwarded from gmail to protonmail doesn't show the attachment.
If I forward the email from my own gmail to my own gmail, thus triggering the autoforward. There's no issue.

The issue seems to be specifically when sending an email from python using yagmail to protonmail.

I'm using this package to send diagnostic emails to users. A user got the following response from Proton Mail support and shared it with me (Neon AI refers to the email sent with yagmail):

1. The "Content-Type" email header field.
 
The correct file name formats seem to be the following:
name="example.txt"
filename="UTF-8 encoded file name"
 
However, Neon AI used the following:
name*=utf-8''voice_log.txt
 
2. The "Content-Disposition" email header field.
 
<Neon AI> should add this field for their attachments.
 
3. The "MIME-Version" email header field.
 
Looks like the "MIME-Version: 1.0" header should not appear in the attachment's email header fields.
 
4. Comparison.
 
Yahoo
Content-Type: text/plain
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="=?UTF-8?b?ZXhhbXBsZS50eHQ?="
Content-ID: <[email protected]>
 
MSFT
Content-Type: text/plain; name="example.txt"
Content-Transfer-Encoding: base64
Content-Description: example.txt
Content-Disposition: attachment; filename="example.txt"; size=4;
    creation-date="Tue, 27 Aug 2024 08:08:55 GMT";
    modification-date="Tue, 27 Aug 2024 08:09:02 GMT"
 
Gmail
Content-Type: text/plain; filename="example.txt"; name="example.txt"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="example.txt"; name="example.txt"
Content-ID: <f_m0c4qkcl0>
 
Proton
Content-Type: text/plain; filename="example.txt"; name="example.txt"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="example.txt"; name="example.txt"
 
Neon AI
Content-Type: text/plain; name*=utf-8''voice_log.txt
MIME-Version: 1.0
Content-Transfer-Encoding: base64

ProtonMail support noted that Gmail handles these headers properly but that they are in an "incorrect format", so it appears they do not plan on handling it on their end.

@NeonDaniel thanks for posting, though from your post it's not clear to me what should be fixed still.

If you make a pull request with the correct format, I can push a new version.

@NeonDaniel thanks for posting, though from your post it's not clear to me what should be fixed still.

If you make a pull request with the correct format, I can push a new version.

I am also not entirely sure what changes are necessary to make the headers match what ProtonMail expects. I will try to find time to dig in though. Glad you're still maintaining this package 🙂