Sorry to not reply sooner. That usually is something the e-mail server is kicking back to us. What I would recommend is trying to isolate the problem down piece by piece since Logicity can't really give you any more details that what it shows here. I would start with a report with just one known to be good recipient and see if that goes through - that will at least tell you that the basic plumbing works. From there, add in your recipients one by one and see where it breaks. Make sure that your e-mail recipients are separated with commas. You might also want to try setting up an e-mail client with the same SMTP settings as Logicity and make sure everything works there. Hopefully something here is helpful.
