Max Suggested Inbound Attachment Size?

Posted on 2012-08-24
Last Modified: 2013-11-22
Right now I have the out-of-box standard for Exchange 2010 of 10.2MB in/outbound attachment restrictions.  Of course, our users are clammering to be allowed to have up to 20MB -- I have TrendMicro's ScanMail for Exchange in place.  What's the maximum suggested attachment size to permit into my environment?  I seem to remember after a certain size, the a/v just delivers it b/c it's too big...but how big is too big?

Question by:NAMEWITHELD12
    LVL 12

    Accepted Solution

    I don't see anything from Trend regarding not scanning attachments over a certain size.  20MB seems reasonable to me if your network and storage can handle it.
    LVL 26

    Expert Comment

    by:Thomas Zucker-Scharff
    We use 20mb as the restricted size but also use an accelion device which takes over from there and stores then sends a link to files larger than 20mb and smaller than 2gb.  The storage is for 7 days with no backup.
    LVL 52

    Assisted Solution

    I would say go for 30MB ..... as messages over the internet expand with 30-35% so if another user send you an email of 15MB it will be arond 20MB when it hits your environment

    I would say anything around 50-60 MB can be termed as BIG :) ..... but again it very much depends on your environment needs :)

    Understanding Message Size Limits

    Exchange 2007 Message Size Limits

    Scope of Limits
    Global Limits
    Connector Limits
    Server Limits
    User limits

    - Rancy
    LVL 13

    Expert Comment

    Years ago (with slow connections) we've implemented a 5 MB limit for the entire mail, resulting in a somewhat lower limit due to transfer encoding.

    On your side there's not any reason besides HDD space and software implementation limits to limit the attachment size.

    On the other side many servers in between your serevers and the mail recipient may have implemented limits on incoming and/or transferred messages (not generally but mostly caused by attachments ... principially a message may have a 30MB body, but that's a rare condition).

    So you might raise the limit up to the desired 20MB, but I would implement a server side filter that sends a warning to your users if their message excceeds a "safe" size. I would recommend something like
    Your message to [recipient's address] exceeds a size of xx MB. Even while we support messages exceeding that size (up to yy MB), some systems in between on the way to the recipient (that are out of our control) might me not that generous. And they might choose to refuse to notify you if your message will be dropped. To be sure that your message was not lost in transit, you might wish to aks for confirmation of delivery by sending another (small sized) message or dropping the recipient a phone call.

    Besides of that you can encourage your user to
    use compression software like Wizip, WinRAR, etc.
    use the file splitting features of the software above (or other, specialized  software like i.e. WinSplit) to split the files into smaller chunks to be sent in separate messages
    use more bandwidth-efficient techniques like FTP
    LVL 7

    Expert Comment

    Another thing to consider -

    Exchange checks the uncompressed size of the attachment. Say if actual size is 10MB exchange will consider it as 10 MB however AV gate might think its 7MB (Compressed). So whatever you decide put less on AV gate side and little higher on exchange.
    LVL 26

    Expert Comment

    by:Thomas Zucker-Scharff
    You also might consider dedup usage in exchange.  In this way you can actually allow larger file attachments since they will only appear once even if say 100 users email the same attachment.

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