I have these set up as 15 groups of 20 and send an email to each group BBC (so members do not get contact details of each other).
Over the last few months I have had problems sending these messages successfully. Although they appear to be sent ok I later find out that many recipients did not get the message (nor is it diverted to their junk folder). It seems that my messages are intercepted before they get to the recipient's pc.
As I do not get messages bouncing back I am unable to tell who has got the message and who hasn't.
It seems to me that because I am sending so many messages with attachments (the walk details include a map of 8kb or so) some systems treat my mail as spam and delete it.
Any ideas how I can get round this problem and send my walk invitations successfully?