I send from Outlook 2016. The other party is running Thunderbird. The recipient (hereinafter "She", "her") complains that most of the time when I send .pdf attachments all she gets is a winmail.dat attachment.

I looked up winmail.dat and see it is just a packet of formatting information to help a limited number of other email clients paint the email on screen.

I considered that it might be security software on her end but she claims that this only happens with my transmissions (She receives .pdf attachments from other people without problem).

I have started to send to an additional person in her office and look forward to getting the results so this posting is likely premature, but I was wondering if this might be a known problem of some sort. I also accept it could be something to do with her configuration or interpretation, for when I once worked in the same office as her she attempted to microwave popcorn and set the timer on for 30 minutes. Lots of black smoke...

Thank-you.

Edit: I forgot to note that sometimes the attachments do make it through without a problem; perhaps 75% of the time not, resulting in retransmission requests. As I am not onsite where she is I find it a little frustrating to track down, like a car that only malfunctions when you are driving it and never when you take it in (OK, so that is more of an "old-timers" problem now with the OBC...)