Emails sent with delay appear twice

[mm3509]

I send emails with delay using mu4e-send-delay. The repo seems out of date with the last commit 2 years ago.

I often find that emails I sent with delay are sent twice, for example a pair sent within 1 minute of each other:

Date: Mon 29 Apr 16:05:09 2019
Date: Mon 29 Apr 16:04:17 2019

an another pair within 1 second of each other:

Date: Tue 30 Apr 12:51:22 2019
Date: Tue 30 Apr 12:51:21 2019

And some pairs have exactly the same timestamp.

Nevertheless, some recipients I contacted only receive one of them.

In addition, attachments show differently, for example one email in the pair has:

Date: Mon 29 Apr 11:56:01 2019
Maildir: /Sent Items
[...body of email...]
<#part type="application/pdf" filename="/var/folders/zx/j_gjm0ld081b_mcqmg3gp9l1zp59y6/T//mu-2137171910/9ca95bbc/3/SS Programme 2019.pdf" disposition=attachment>
<#/part>

and another in the pair has:

Date: Mon 29 Apr 11:55:41 2019
Maildir: /Sent Items
Attachments: [1]SS Programme 2019.pdf(1.1M)
[...body of email...]

[mm3509]

The problem is due to IMAP. The email is written to the Sent folder once upon sending and then again when pulling emails from the server. Hence the discrepancy in times and in the appearance of attachments. See also a thread on Emacs StackExchange.