I am not really sure if this question belongs here as I am not convinced if it is Outlook but server related. Anyway...
The problem is with an Outlook 2003 installation (latest updates, all patches) which runs on a XP Pro notebook (Acer C300 Tablet PC) without any problems unless... This Outlook only uses POP3 (resp. some IMAP4) accounts and sends via SMTP servers (no SSL in both directions, except a Gmail account).
I travel a lot and sometime to remote areas and developing countries where one has to be lucky to find a connection to the Internet. It seems the slower (not unstable!) the internet access is the more I run into troubles.
It is more or less impossible for me to send emails with attachments larger than one or two MB. What happens is that Outlook starts sending (you can see from the connection icon in the task bar that something is happening) and after some time it simple stops, Outlook gives a brief error message in the status bar (which immediately disappears again) and the email remains in the Outbox without being sent. Smaller attachments work without problem. Back in Europe with my 6 MBit xDSL I have no problems sending 10 MBs or more...
My problem is to explain it in detail because I can't really fully reproduce it. What I think I found out is that it must be somehow related with the time the client is connected to the server. Because if I use a fast uplink connection the amount of data I get through is higher.
Two examples and observations:
(1) Connection (permanent, fixed IP) approx. 16kbit/s UP and 48kbit/s down, location in Africa, backbone via satellite
SMTP servers (I tried several different servers around the world to be sure) located in W-Europe and US, connected via a premier ISP, so definitely no problem from there.
Receiving from any POP/IMAP account actually no problem, even if attachments are large. Only problem also RECEIVING from Gmail when email is largen than approx. 1.5 MB. Same behavior like sending. Just stops and restarts according to send/receive schedule.
SENDING a pain with any attachment largen than a few Hundred KBs. Simply does not get out, remains in Outbox. Funny enough, although it sometimes does not seem to go out it is actually sent out and so it happens that the mail is sent over and over again because Outlook believes it did not go. Some recipients do not greet me anymore after 25 times having received the same email over and over again :-)
(2) Connection (wireless via UMTS) approx. 40kbit/s UP (effective) and 128kbit/s DOWN (effective), location in Africa, backbone via satellite
Same behaviour here although amount of data getting through is larger. I can get out approx 3MB and down up to 6-7 MB but above that also no chance.
I have, of course, tried all the settings in Outlook, Windows network settings etc. without success. Also disabled all firewalls, spam filters, virus scanner etc., also no luck. I also tried another client (Thunderbird) which has the same behaviour so this leads me to the assumption it has something to do with the mail servers.
One of the mail servers (a CommuniGate Pro located in Austria) is operated by myself. Works like a charm normally but also the same problem when I connect from a slow connection. At least I have access to all the settings on this server so if someone has any idea on the server side I can play around there.
The actual question now: what is this problem and how can I avoid it?
Any advise appreciated because it really affects my work and nerves!!!