Not all emails being received?

Hi,

Could anyone offer any assistance with an issue I'm having with my VM email account, which is an old Blueyonder one. 

Emails are being received however not all, I've specifically been waiting for an urgent email to arrive, with an attachment. The sender has tried sending a number of times but still hasn't appeared and no indication it has been classified as spam.

Could this be being blocked by VM possibly due to the size of the attached or would there be any other reason why it it may not have appeared as it does seem odd and we're sure the sender has the correct email address.

Thanks for any help?

Regards,