Word to the Wise maintains these ISP reference tables for the benefit of senders and systems administrators working to improve email delivery.
The “Sender Support” table below offers a quick reference to various ISP postmaster pages, FBL pages and unblocking pages. The second table, “Delivery and Filtering Details”, lists known connect limits, spam filters and certification services.
Sender Support
Delivery and Filtering Details
A little more information about the specifics of delivery at various ISPs. Note that the “does not publish” for limits means that the ISP has said they have limits, but they do not publish those limits specifically. Many of these ISPs tie sending limits to reputation; IPs with poor reputations have much lower sending limits than IPs with good reputations.
| ISP | Connection Limits | Sending Limits | Certification | Reputation Providers |
|---|---|---|---|---|
| AOL | 500 emails per connection 100 recipients per message |
Return Path Certified | ||
| AT&T | no published limits | no published limits | Return Path Certified | |
| Bellsouth | no published limits | no published limits | ||
| Charter | no published limits | no published limits | no confirmed | |
| Comcast | 25 connections per IP address | 100 recipients per message | Return Path Certified | Spamhaus Spamhaus ZEN Cloudmark CSI Return Path Reputation Network Blacklist. |
| Cox | 5 connections per IP address | 100 messages per connection | Return Path Certified | Spamhaus Zen Return Path DNSBL Invaluement SIP list Cloudmark CSI SURBL Spamhaus DBL Invaluement URI list |
| Earthlink | does not publish | does not publish | no known certification services | |
| Excite | 10 per IP | 10 per connection | Return Path Certified | Cloudmark CSI blocklist Spamcop blocking list Return Path Senderscore blacklist internal |
| Fastmail | Spamhaus XBL Spamassassin |
|||
| GMX | ||||
| Gmail | does not publish | not using any | ||
| Hotmail | based on the reputation | based on the reputation | Return Path Certified | |
| Integra | no published limits | 100 emails per address | ||
| Juno | ||||
| Live.com | ||||
| Mail.com | very little information available | very little information available | has not published | |
| Mail.ru | ||||
| Netzero | ||||
| OpenSRS | ||||
| Outlook | 500 simultaneous connections | |||
| 1 connection per IP | 1 email per connection | |||
| Rackspace | very little information available | very little information available | Return Path Certified | has not published |
| Roadrunner | do not publish | do not publish | Return Path Certified | Spamhaus ZEN Return Path Reputation Network Blacklist |
| Synacor | ||||
| Terra.com.br | ||||
| Time Warner Cable | ||||
| Tucows | very little information available | very little information available | Return Path Certified | has not published |
| United Online | ||||
| Usa.net | does not publish | does not publish | Return Path Certified | Cloudmark |
| Verizon | Return Path Certified | not known to use | ||
| Yahoo | 20 emails per connection reputation based rate limiting |
Return Path Certified | Spamhaus XBL Spamhaus PBL |
|
| Zoho |
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Zoho and Terra aren’t on your list. Big or small, FBL is FBL 🙂
https://fbl.zoho.com/
http://fbl.mail.terra.com.br/?lang=en_US.utf8
Turned off comments because of the thousands of spams I was having to clean out daily.
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