I am not aware of an issue with pages files but they may not be supported as they are not that common. A quick solution would be to drop the pages file in a folder and then zip it (compress it).

Thanks, we'll try that. The sad thing is, we use Pages instead of Word, and having to put every file into a folder and zip it, before attaching it, is going to become cumbersome on both ends.

What attachment procedure are you using? e.g.

File|Attach drag and drop toolbar button

…or some variant of "send to…" from an OS menu?

A file is a file. If a Pages document is a simple file, then if you're using any of the first three "normal" techniques I can't see why TB should have any basis to refuse it. "Send to…" is a different kettle of fish…

Having never used Pages, I don't know what a Pages file looks like. Is it truly one monolithic file, like a doc or pdf file? Or is it like a web page, with a parent document and a passel of accompanying files? You can't easily send such assortments as attachments in Thunderbird without binding them together. I am aware that some email clients seem equipped to do this sort of thing for you…