| features/software | aweber | mailloop | postmaster | emailer2001 |
| number of autoresponders | 6 | unlimited | unlimited | unlimited |
| personalized e-mails | yes | yes | yes | yes |
| html format | yes | yes | yes | yes |
| custom fields | no | yes | yes | yes |
| unlimited lists | no | yes | yes | yes |
| undeliverables handling | yes | yes | yes | yes |
| bypass isp's smtp server | use of their own | yes | yes | yes |
| multithreading technique in sending emails | no | no | no | yes |
| price | $179.40 (anually)* | $379 | $349 | $127 |
* The Aweber is a server-side program, and runs from their site. Therefore you 'll have to pay for it periodically.