SMTP

Enabled by default: SMTP Tarpit in Exchange Server 2007

From a recent discussion, and something I’ve been wanting to post about for a while: SMTP tarpitting is enabled by default on Receive Connectors in Exchange 2007 (and Exchange 210). What is SMTP tarpitting? It’s the process of introducing a delay in SMTP connections from hosts that are suspected of inappropriate SMTP behavior – for […]

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SMTP Virtual Servers: Some irksome defaults you should change

The SMTP stack provided by IIS’ SMTP svc in Exchange Server 2003/2000 changes significantly when Exchange is installed on a Windows server. Some ESMTP extensions are added to support Exchange, it gets Exchange’s Advanced Queuing Engine (AQE) implemented in phatq.dll, and the Categorizer (phatcat.dll). The mailroot path is moved from IIS’ default (\inetpub\mailroot) to \exchsrvr\mailroot. […]

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How To Allow Relaying in Exchange 2010 and Exchange 2007

In Exchange Server 2003, you can allow anonymous SMTP hosts to relay mail by adding their IP address(es) in SMTP Virtual Server Properties | Access tab | Relay. Hosts that require anonymous relay capability include application servers and devices such as copiers, which scan documents and send them as email attachments. Figure 1: Controlling relay […]

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Should MX record point to CNAME records (aliases)?

Though the practice of pointing MX records to CNAME (alias) records is not that uncommon, it certainly isn’t in keeping with internet standards. When you point a MX record to a CNAME, you’re in fact inviting double the DNS traffic to your DNS servers. Try this by performing a name resolution query using nslookup: >nslookup […]

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HOW TO: Prevent sending display names with internet messages

Exchange Server and many other MTAs including most web-based services send the sender’s display name (e.g. “Joe User”) in email messages, in addition to the smtp (email) address. If you want to prevent sending display names in outbound internet mail for any reason, you can turn this off. Exchange Server 2003/2000 (Exchange System Manager):– Global […]

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RFC 2821 and the “implicit MX” rule: Can you really get mail without an MX record?

This question has been asked frequently enough, so it makes sense to clarify another SMTP myth that many IT folks hold dear: No MX records = no email Yes, mail can indeed be delivered to a domain even if it does not have MX records. Let’s take a look at what RFC 2821 says:– Once […]

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Microsoft opens up SenderID

Microsoft announced today it’s putting its SenderID technology under its Open Specification Promise program. This allows anyone to create products or services using SenderID technology. SenderID lets (receiving) mail servers determine whether a sending mail host is authorized to send email for a particular domain, based on SPF records published in the sending domain’s DNS. […]

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Message Tracking from the command line in Exchange 2010 and Exchange 2007

I’ve forever envied folks (including some colleagues— you know who you are… ) on the Linux/Unix side of things who were able to parse text log files generated by MTAs like Postfix/SendMail/EXIM in a fraction of the time it takes one to fire up Message Tracking Center on Exchange and search for a message. I […]

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Logging SMTP protocol activity

Like many of my posts, this one also starts with “By default,… “. Like many folks, I’m always curious about the defaults used for almost everything in Exchange/SMTP (and IIS, Windows, AD et al), and at times intrigued by the choices made. One of my pet peeves has been about how installing Exchange changes the […]

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Address Literals and Microsoft Exchange

RFC 2821 specifies how address literals can be used to reach recipients – particularly useful when DNS resolution doesn’t work for a particular domain or host. This is a literal form of the address which can be used as an alternative to the domain name. For IPv4 addresses, the address literal format is localpart@[1.2.3.4] – […]

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