Attachments missing signatures

[apiote]

From time to time (but it happens only when there’s at least 1 attachment; i.e. apart from message body) I get the following error:

msmtp: the server did not accept the mail
msmtp: server message: 554 Error: transaction failed, blame it on the weather:
cannot send message: [15197] One or more attachments is missing a signature
msmtp: could not send mail (account {account name} from {config file})

[SillyPilleus]

I have hydroxide set up as a network bridge to forward notifications on from servers on my network which do not have official bridge clients available for them. They send out log files as attachments though, and I'm getting this error every time I want to send an attachment... I certainly do not have the skills to fix a bug like this, but I'd love to see it squashed as I can then use Protonmail for all my notifications!