Turn off SPAM and Virus Filter

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I have added a lot of users recently, causing my server to bog down a bit. I am running a 3rd party SPAM and Virus filter so I figured the first thing I could do was turn off AS/AV on Zimbra. I went to Global Settings AS/AV tab and unchecked "Enable spam checking and antivirus" and clicked save. After I did that it seemed mail was not being delivered. When I enabled the service, mail began to flow again. Is this no the proper way to turn this off or is there more to it? Thanks for any help.

[telescop]

I really don't want to open a support case for this. Thanks for any info.