Exchange: Setting SMTP max mail sizes in mail flow

Exchange: Setting SMTP max mail sizes in mail flow

Default size is 10MB and that is just how it should be. Even if freeware mail provider has, 50MB Limits. It is not a law but its historical SMTP/RFC value from and people have lived with it for 15 years. Then some nerd put it up 5MB and others had to follow.

Everyone who lets an e-mail attachment larger than 20MB in the www should be blocked and blacklisted.

Use FTP, SharePoint or a commercial Data room solution (Not free stuff) if you are too stupid for ZIP or Splitting ZIPS.

Find all users in Exchange who have special Sizes:

Get-Mailbox -FIlter {MaxSendSize -ne $null -OR MaxReceiveSize -ne $null} | ft Name,MaxSendSize,MaxReceiveSize

Per User in GUI:

Per Exchange Organisation with Powershell:

Set-TransportConfig -MaxReceiveSize 50MB -MaxSendSize 50MB

These are per attachment size settings:

set-transportconfig -ExternalDsnMaxMessageAttachSize 40mb -InternalDsnMaxMessageAttachSize 40mb
get-TransportConfig | fl

On the separate Receive Connectors:

Here is a logfile:

Here is how to check the Sizes with telnet. Make sure your Mcafee or other virus Software does not block SMTP/Ports25 from test client.

Do not forget to check the SIZE on your in-house SPAM Filter

Exchange will DROP the e-mail IF you have a mismatch in the size in your internal network. As example, if you have a Fortimail 100, an Exchange 2010, and the sizes are different. Fortimail will not re-try internal per default.

You will lose that e-mail!

Some links:

http://exchangepedia.com/2007/09/exchange-server-2007-setting-message-size-limits.html

 Text from RFC and why it’s OK some device just drops the email which is too big.

http://tools.ietf.org/html/rfc1870

6.2  Client action on receiving response to extended MAIL command

The client, upon receiving the server’s response to the extended MAIL
command, acts as follows:

(1) If the code “452 insufficient system storage” is returned, the
client should next send either a RSET command (if it wishes to
attempt to send other messages) or a QUIT command. The client
should then repeat the attempt to send the message to the server
at a later time.

(2) If the code “552 message exceeds fixed maximum message size” is
received, the client should immediately send either a RSET command
(if it wishes to attempt to send additional messages), or a QUIT
command.  The client should then declare the message undeliverable
and return appropriate notification to the sender (if a sender
address was present in the MAIL command).

A successful (250) reply code in response to the extended MAIL
command does not constitute an absolute guarantee that the message
transfer will succeed.  SMTP clients using the extended MAIL command
must still be prepared to handle both temporary and permanent error
reply codes (including codes 452 and 552), either immediately after
issuing the DATA command, or after transfer of the message.