Sending Attachement Timesout

[mickalo]

Hello,

we have a customer that has no problems sending out emails, except when they add a file attachment. They sent one today with a 240kb file attachment this was the error message they got.

 Your server has unexpectedly terminated the connection. Possible causes for 
 this include server problems, network problems, or a long period of 
 inactivity. Subject 'Fw: test', Account: 'mail.investordataexchange.com', 
 Server: 'mail.investordataexchange.com', Protocol: SMTP, Server Response: '421 
 justlightening.justlightening.net SMTP incoming data timeout - closing 
 connection.', Port: 26, Secure(SSL): No, Server Error: 421, Error Number: 
 0x800CCC0F

I can not find anything in the logs that would shed light on the problem on our server so I am assuming this is a problem on their end. They use their "mail.domain.com" as their outgoing SMTP mail server, using both port 25 & 26 and get the same timeout error. But no problems sending out emails w/o an attachment? I sent out an attachment through our mail server with PDF approx., 1MB in size with no problems. So I am assuming this is a problem on their end or internet connection ??

Any help or suggestions would be much appreciated.

TIA,
Mickalo