A business customer rings with an odd outlook email problem: it keeps resending emails (multiple times)… which make the company look unprofessional to the recipient.
I do my usual badware & virus check, but find nothing (laptop already has the trend antivirus). So while the ewido scan is in progress, I do some ping tests & notice ping times around 1000 to 2000 ms (to google.com.au)… they should be around 200 to 300 ms.
I notice the telephone cable is plugged into one of those surge-protector boards. I bypass that, just to eliminate it from the equation… but nothing changes.
I then shutdown outlook, & everything is quick again…hmmm.
I look at the email sitting in the “outbox” folder, & it has an 8MB attachment… A touch large for an email attachment… it’s a tif image from a scanned image… and smaller emails go through without a hitch.
So I check out the ISP (telstra bigpond), to see what kinds of limits they have on their SMTP servers… there doesn’t seem to be any size limit, but after some more digging, I find some obscure references to a 20 minute smtp limit… ie if you can send an email within 20 minutes, fine (so the faster your internet connection, the larger the attachments you can send).
I suspect that if the email takes longer than 20 minutes, then the smtp server just truncates the email & sends it “as is”… At the other end of the connection, Outlook (or should it be called “Lookout!”?) gets an error message, so it shrugs it’s shoulders & tries again (thus multiple emails get sent).
Now I do some simple sums: assuming a slow adsl connection: 64kbitsps uplink, and a 9Mb email (90,000 kbits), then the email should take 90000/64 =1400 sec =23 minutes… but a faster adsl should not have a problem with this… and the customer is unsure of the adsl speed.
I also notice that trendAV also scans email (incoming & outgoing)… So scanning outgoing emails could slow things down a lot… I disable the outgoing AV scan… & I suggest that they try to keep attachments to below 2 or 3 Mb. Outgoing emails now work fine, as long as the email size is kept to something reasonable.
Everything else is fine… I find some spyware running on a second computer & install some anti-badware measures.