SMTP

Net neutrality and how ISPs can impact your email security

There was a time ISPs limited themselves to providing layer 3 connectivity. You got a connection, and if the link was up and your computer or network configured correctly for Internet Protocol (IP) communication, you could send and receive TCP/IP packets over that link. The ISP controlled the bandwidth, which is the maximum rate at […]

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Export and Import Content Filter Words or Phrases

In Exchange 2010 and Exchange 2007, you can add custom words or phrases as good or bad words to modify the Spam Confidence Level (SCL) assigned to messages. Messages with a good word or phrase are assigned an SCL of 0 and bypass other antispam agents that fire after the Content Filtering agent. Messages with […]

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Removing internal host names and IP addresses from message headers

Another frequently asked question about SMTP mail – how can I remove internal host names and IP addresses from outbound Internet mail? More often than not, this results from the belief that somehow if the outside world finds out an organization’s internal IP addresses and host names, it makes the organization vulnerable. Auditors love to […]

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Masquerading SMTP Virtual Servers: Changing the fqdn and masquerade domain

You can change the fully-qualified domain name (fqdn) used by a SMTP virtual server from its properties | Delivery tab | Advanced | Fully-qualified domain name. In the following example, we change the fqdn of a SMTP virtual server from its default – letter.exchangelabs.net, to postcard.exchangelabs.net. Figure 1: Changing the fully-qualified domain name in SMTP […]

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Set Message Size Limits in Exchange 2010 and Exchange 2007

In Distribution Groups and maximum recipients per message, we looked at how the maximum recipients per message settings are treated differently by Exchange Server 2010/2007 and Exchange 2003/2000 when sending to Distribution Groups. Message size limits are an important mechanism to control mailbox sizes, guarantee service availability, and protect from potential DoS attacks. Another commonly […]

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Connection Filtering, RBLs and SMTP logs in Exchange 2007/2010

Exchange Server 2003’s Connection Filtering feature allows you to block connections from IP addresses explicitly added to the Global Deny List, or drop messages from IP addresses listed on a RBL (Real-Time Blackhole List / Real-Time Block List). Note: The term “RBL” is commonly used to describe DNS Black Lists (DNSBLs), but it’s a trademark […]

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Address Literals in Exchange 2007 and Exchange 2010

RFC 2821 allows the use of a literal form of a recipient’s address, which uses the destination system’s IP address enclosed by square brackets in the domain part, as an alternative to a domain name. Commonly known as address literals, this form of addressing helps in delivery of mail to a recipient when the recipient’s […]

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Logging SMTP Protocol Activity in Exchange 2013/2010 and Exchange 2007

I wrote about logging SMTP protocol activity in Exchange Server 2003 in what is one of the most popular posts on Exchangepedia. Starting with Exchange Server 2007, Exchange discontinued using the SMTP stack in IIS and developed its own SMTP stack. I like to think of it as smarter or more intelligent Receive Connectors (these […]

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Protect users from spam from your own domain in Exchange 2010 and Exchange 2007

One of the common complaints from users and many messaging folks is spam received from senders that appear to be from your own domain. SMTP mail is exchanged with anonymous Internet hosts without any authentication. Headers can be and are effortlessly spoofed. Rather than using an unregistered or invalid domain in the From: header, many […]

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RFC 2821, HELO again: Validating the HELO/EHLO domain

RFCs 2821 and 1869 specify the format of HELO/EHLO commands issued by a SMTP client to initiate a SMTP session. RFC 2821 on HELO/EHLO command: 4.1.1.1 Extended HELLO (EHLO) or HELLO (HELO) These commands are used to identify the SMTP client to the SMTP server. The argument field contains the fully-qualified domain name of the […]

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