send attachment txt file fails

[leffss]

Thanks for your great work on yagmail. I'm running yagmail-0.15.277 on python 3.9(both windows 10 and Linux(centos 7.9) have been tested).

I send attachments like this:

...
attachments = ['main', 'main.py', 'test1.txt', './test.png', 'test2.txt', 'test.zip', 'test.py', 'notest']
yag.send(to=receivers, cc=CC, subject=subject, contents=[body, html], attachments=attachments)

I test send mails to alimail(https://qiye.aliyun.com/)，qqmail(https://mail.qq.com), 126mail(https://mail.126.com) and gmail.

This email arrives just fine，and all the attachments find in 126mail(https://mail.126.com) and gmail.

But without txt file attachments(test1.txt and text2.txt) in alimail(https://qiye.aliyun.com/) and qqmail(https://mail.qq.com).

And I did some troubleshooting on alimail(https://qiye.aliyun.com/), qqmail(https://mail.qq.com) and found：

• If test1.txt and test2.txt file size >= 22bytes，qqmail(https://mail.qq.com) become available to receive the txt attachments
• Anyway the alimail(https://qiye.aliyun.com/) can not receive the txt attachments

Final，if use smtplib and email to send txt attachments, all the mailbox can receive the txt attachments.