The default size limit on the webmail facility is 10Mb.
It is however 25Mb on a standard lite account on a mail client, this is however subject to swelling of upto 40% so anything over 15Mb, can be an issue.
As the email travels from the BT server to the destination server, it picks up header and other information from each server in the journey this adds additional information into the email to a maximum of 40% depending on the path of the email.
I'm not overly sure about this, but having a read around it seems that attachments can be coded and decoded by base64, this can lead to a considerable increase in the size of the message.
If you send an email over 20 hops or 300 the encoded message does not increase in size. Some hops may reject attachemnts over a certain size on the way. Besides a 10 meg attachment should be FTP'd or uploaded to a file server and not clogg up the mailbox cash while trying to send over the inherently slow connections we have in this country.
I have seen instances where 18Mb attachments will not send through BT's servers, the server logs here showed something similar.
This was however on the old server 2003 run by BT not the new platform, although they are sticking with the 25Mb limit for the timebeing for lite users.
Although sending files of this size ideally should be done through methods such as ftp.
