I'm having the same issue here, KMail Version 5.9.3, but with 2.9MB. This is the only match for my search for "Share it with storage service" in Google, for which I guess it might be some weirdness because if this limit existed more widely I guess I would have found lots of matches, but any help on debugging this is appreciated.
The complete error message is: You may not attach files bigger than 2.9 MiB. Share it with storage service. -- Leandro Lucarella (Luca) https://llucax.com
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