Your Email is Subject to Spam Filters

Most people don't think about it, but nearly all email is now subject to some processing by spam filter software. If it's important that a given piece of email gets delivered, you should think about this before sending it.

Spam has impacted email reliability in several different ways. One is the signal-to-noise-ratio. If your email is buried amongst 190 pieces of spam, there's a good chance the recipient may not ever get around to reading it. The other primary concern is errant filtering, also known as false positives.

False positives do happen, but they are a lot more prone to happen to certain kinds of email. For most systems, the exact method of blocking messages is not public knowledge. However, there are some basic guidelines that can often help improve the odds of your email actually making it to the recipient.

Don't use large amounts of HTML in your email message.

Don't embed images in your email.

Avoid including large URLs within your message. This goes double for long URLs, or URLs including parameters such as search strings.

Email customization products like Incredimail or Hotbar tend to do all of the above. Try to avoid using them. Besides, your friends don't really want to see pictures of your grandchildren included with each email. Applications that try to do stunts like verify an email has been received can also set off email spam blocker alarms.

Free web-based email services also tend to add HTML and URLs to your messages. They can also be problematic for message filtering systems. Some users also tend to block email from domains such as Yahoo! and Hotmail.

Messages making references to financial issues, pharmaceuticals or adult content are more likely to be heavily scrutinized. While avoiding these topics may not be an option, take extra care to observe the prior suggestions when mentioning them.

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