This bug sometimes results in sending read receipts to self in
multi-device setups.
It happens consistently in a setup where the first device is
configured to move messages to DeltaChat folder and the second device
is not. When both devices receive BCC-self message simultaneously, the
first device moves the message to DeltaChat folder, while the second
device tries to mark the message as seen in the Inbox. Regardless of
whether the second device marks the message as seen successfully or
fails because the message is already moved by the first device,
`Job.markseen_msg_on_imap()` sends the read receipt to the From
address.
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