Are your users really so sensitive to the specific attachment limit?
Whatever you set it at, you will always get one who has an "important
document" that is just that bit bigger.
Anyway, base64 encoding incurs a 33% overhead, so to set a 25MB limit as
seen by the user, you need to tell Exim the limit is 34MB or so. And be
vague to end users about the exact size, and instead emphasise other
methods of large file transfer.
Jethro.
On Tue, 8 Sep 2015, Osborne, Paul (paul.osborne@???) wrote:
> Hi,
>
> I have been playing with message size adjustments and I have noticed
> that when setting Exim's message_size_limit = 25M I would expect
> messages no bigger than 25 MB through.
>
> However I sent myself a file through to test this:
> -rw-r--r-- 1 po35 po35 24021574 Feb 15 2015 test-pdf.pdf
>
> Which is about 23MB in size and so was somewhat confused that when it got to Exim to find that I got the following message:
> message too big: size=32873715 max=26214400 (25MB)
>
> So whilst I appreciate some growth where the attachment is re-encoded
> and packaged up to be sent via email I was to be honest mildly surprised
> that there was a 25% growth in attachment size. I am not going to be at
> all surprised if someone tells me that this increase can vary dependant
> on the encoding method and the type of data etc etc - but it does make
> things a bit of a pain when I need to advertise a hard figure as a
> maximum size that we will allow through our mail system when that does
> not correlate to what the user sees as a file size usage on their disk.
>
> Short of picking a number such as 35MB for Exim's benefit and hoping
> that is enough as I can live with going over the threshold but under is
> not going to make me popular, does anyone have a better way of
> calculating what I need to set the limits to to ensure a 25MB attachment
> can get though (no matter what the encoding etc)?
>
> Cheers
>
> Paul
>
>
>
> Paul Osborne
> Senior Systems Engineer
> Canterbury Christ Church University
> Tel: 01227 782751
>
> --
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> ## Exim details at http://www.exim.org/
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. . . . . . . . . . . . . . . . . . . . . . . . .
Jethro R Binks, Network Manager,
Information Services Directorate, University Of Strathclyde, Glasgow, UK
The University of Strathclyde is a charitable body, registered in
Scotland, number SC015263.
