Phplist sends more email than it should

Phplist sends more emails than it should at least this is what I see in the campaign report.

Also it seems it will never stop sending a campaign. Recently it sent over three times more emails to a list of only 800 emails. I had to stop the sending process.
My version is 3.5.5 and I’m sending campaigns from within the application.

This happens since one or two weeks ago. Previously everything worked just fine.

Thank you.

I found this in the log event: Error sending email to SMTP Error: data not accepted.SMTP server error: DATA END command failed.

I am not sure what is this. It seems no emails were sent at all.