Example of blacklisted ESP

If your IP address is blacklisted, it may explain low or declining email delivery rates. Is your your domain or IP address blacklisted? Have you checked?
Have you checked your ESP - Email Service Provider?

As a legitimate email marketer, you have to be concerned if your IP addresses are blacklisted on various dns blacklists and blocklists. If an IP address is blacklisted, email delivery rates decline as mail servers filter your email. To ensure opt-in emails are being delivered, it is crucial to monitor your IP addresses and use a CAN-SPAM or similar (in the EU and elsewhere) compliant email marketing software.

What are DNS blacklists and blocklists?

A dns blacklist or blocklist is a database containing known internet addresses (or IPs) used by individuals or companies sending spam. Various ISP’s and bandwidth providers subscribe to these DNS blacklist databases to filter out spam sent across their network or to their subscribers.

Some of the most widely checked DNSBL blacklists (DNS-based lists) are Spamcop, MAPS blacklist, and SPAMHaus - our Blacklist Monitor^TM checks against these blacklists and many more.

Several tools exist to help you monitor your IP addresses and domains:

Blacklist monitor: www.blaclistmonitor.com
Blacklist MonitorT is a real-time service to monitor your IP addresses. Know when you are listed, where you are listed, and what to do to start the removal process.

SPAM database look-up
Look-up tools enable you to check if an IP address appears on many of the major spam lists.

Try out DNS Stuff: http://www.dnsstuff.com

And while we are at it, you might also want to preview what your “from” and “subject” lines will look like in popular email browsers.  I’ll check for some ressources that will allow you to do just that - for free - and post the ressources here once I find them. (Lyris and others does offer this service, however requires registration, which can be a bit of a nuisance for some of ya’ll).