Can you post a rough translation in English of the error message? Is this an IMAP or POP account? What domain is your email account, such as Outlook, Gmail, or other? Knowing that, someone here may have suggestions. Thank you.

I have a problem saving messages in the "sent folder".

I have this message:

The message was sent but no copy was placed in the Sent folder due to network or file access errors. You can try again or save the message locally in "Local folders/sent-..............@o2.pl".

Unfortunately, this sometimes happens to many people, including to me. And the message may be true. That is, sometimes network problems interfere, especially for IMAP accounts because the network must accept sending the email message and also send a copy to the sent folder. If it happens all the time, I suggest contacting your email provider about network support.

Thank you for your help.