Since I purchased and started using SpamSieve I have encountered the following Phenomenon:
Every once in a while, but several times a day, a message that I had sent maybe a few hours ago, reappears in the Drafts folder. I will check on it, and it was actually sent and is in the Sent box. In the beginning I would resend it to be sure, but once people started complaining about duplicate mails, I knew they would send out okay.
I have no clue if this is related to your product or how Mail’s rule work, but I thought I bring it up to see if it does. I am trying to monitor it a bit better, but it’s hard since mail is received in the background. Meanwhile I do believe it’s related to the fact that mail is being sent and received at the same time, it only seems to happen when there was also incomming mail. Since I get loads of spam, I wonder if the incoming rules maybe hold up whatever process it is that moves the mail from Drafts to Sent.
I really have no clue, if anyone knows anything about it, I’d love to hear about it.