Ensuring requested opt-in email is delivered to subscriber inboxes is an increasingly difficult battle in age of spam filtering. Open and click thru response rates can be dramatically affected by as much as 20-30% due to incorrect spam filter classification.
Confirming that people who ask for your information have actually requested to be on your list is number one step in battle for deliverability. You should be using a process called confirmed opt-in or verified opt-in to send a unique link to attempted subscriber when they request information. Before adding person to your list they must click that unique link verifying that they are indeed same person that owns email address and requested to subscribe.
- Subscriber Addresses
When requesting website visitors to opt-in ask for their "real" or "primary" email address instead of a free email address like Yahoo or Hotmail. Free emails tend to be throw away accounts and typically have a shorter lifetime than a primary ISP address.
- List Maintenance
Always promptly remove undeliverable addresses that bounce when sending email to them. An address that bounces with a permanent error 2-3 times in a 30 day period should be removed from list. ISP's track what percentage of your newsletters bounce and will block them if you attempt to continually deliver messages to closed subscriber mailboxes.
- Message Format
Usage of HTML messages to allow for text formatting, multiple columns, images, and brand recognition is growing in popularity and is widely supported by most email client software. Most spam is also HTML formatted and thus differentiating between requested email and spam HTML messages can be difficult. A 2004 study by AWeber.com shows that plain text messages are undeliverable 1.15% of time and HTML only messages were undeliverable 2.3%. If sending HTML it is important to always send a plain text alternative message, also called text/HTML multi-part mime format.
Many ISP's filter based on content that appears within message text.
- Website URL: Research potential newsletter advertisers before allowing them to place ads in your newsletter issues. If they have used their website URL to send spam, just having their URL appear in your newsletter could cause entire message to be filtered.