In October 2014 I started using Sonicwall's Comprehensive Anti-Spam Services (CASS). Up until the end of May 2015, my company's emails were flowing in and out nicely. I began to field sporadic complaints, from employees, that emails sent to us from other companies were not arriving, at least not in a timely fashion. They did finally arrive, but it could be anywhere from a 1 to 4 hours from the time they were sent. The delayed emails always have attachments and generally range from 2 megs to 10 megs. In the mean time the same sender could and did send the same recipient emails without attachments which rocket right in.
Now the problem seems to be a regular occurrence so I've began troubleshooting it, but I cannot isolate the source. Below is what I'm running:
* Exchange Sever 2003 (no laughing please - I'm going to migrate to 2010 soon!)
* Sonicwall NSA 3500 (SonicOS Enhanced 18.104.22.168-22o firmware).
* Internet service is Comcast business class cable modem 150 down / 20 up.
* About 100 employees
During my troubleshooting I have observed that this problem seems to only occur starting anytime between 9:00 to 10:00 am and usually clears up around 2:00 to 3:00 pm. (Our business hours are 8:00 am to 5:00 pm) Weird I know, so my initial thoughts are bandwidth. I starting checking my Internet speeds and found a problem, our upload was about half what it should be. Called Comcast, they confirmed our area had a problem which they resolved in less than a day. They also sent a technician out who confirmed our modem is working fine, our signal strength is good and test the connection at our site.
Further after hours I can 20 meg emails inbound and receive them in 2 minutes or less.
In exchange under my "default SMTP Virtual Server" I see the inbound sessions from the Sonicwall and when all is working well there are 2 or 3 sessions with times less than 100 seconds. When the problem is occurring there will be 5 or more sessions with much higher numbers like 600 to over 1,000 seconds and I know this is not normal. In exchange I have logging enabled for the default SMTP Virtual Server but because the inbound connections are all from the Sonicwall they is no way to follow through the conversation of an email. I do see some timeout with a code of 121, but again cannot see which email / connection it is related to.
I'm thinking somewhere in the Sonicwall's logging or dianostics in the Dashboard I can find something that might point me in the direction to solving this problem. I am not a Sonicwall guru and when I call Sonicwall it is pure torture so I was hoping you could help.
Finally, I have considered it just too much traffic for our cable based Internet so it may be time to consider moving to a dedicated fiber based Internet connection. Although when we are experiencing the email problem, the Internet runs just fine, it's not slow, I can upload and download just fine. So if it is in fact an Internet connection or bandwidth issue, it would be great to have concrete evidence to present to my company's owners.
Thank you in advance for any assistance you can provide.