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December 8, 2006

IIS SMTP Drop Directory Limitations (Max Size)

This is a brief synopsys of a customer’s problem when using Chilkat SMTPQ with Microsoft’s SMTP server. It is reproduced with permission from the customer:

The Problem:
"… the IIS virtual server stops accepting messages at about 1900 or so. Well I found out that it actually stops after the folder size of \inetpub\mailroot\drop exceeds 20MB.

We had initiated a job with 4000 emails using a single thread. It was going to take about 2 hours, so I mailed an 18MB attachment to that ‘fake’ domain and as soon as it got into the drop folder, IIS stopped taking more messages.

I’m digging around to find some documentation about that but cannot. I’ve screenshot my SMTP server setup, and verified that I have no disk quotas enabled on that drive… Any other ideas?"

The Solution:
The test domain we had setup was a type “Alias” which gathers its settings from the Default domain when you create the virtual server. The only setting you can change on the default domain is “Enable drop directory quota”, which is set to “10 times the size specified by the Limit message size to (KB) setting.” The default setting on the server is 2048KB, but even with that setting disabled on the virtual server, the drop directory still uses 10X that value as it’s quota limit (which jives with the 20MB cap we were hitting).

So the solution would be either:

a) Set the message size to a very large number and enable the limit.
b) Disable the “Enable drop directory quota”

We’re going with b) for now, but it’s all really moot since in production these emails shouldn’t be going to the drop directory anyways.

(I’d like to express my gratitude to the customer for allowing Chilkat to reproduce this information.)

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