ISP Information

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

ISP Postmaster site Feedback Loop Whitelist Support
AOL Postmaster Website FBL signup Whitelist Signup AOL support pages
AOL Postmaster Blog
AT&T Postmaster pages does not offer does not offer SMTP errors list
Blocklist removal form
Bellsouth (AT&T) does not offer does not offer
Charter Postmaster pages does not offer does not offer
Comcast Postmaster pages FBL Signup does not offer Blocklist removal form
Cox Postmaster pages FBL Signup does not offer Blocklist removal form
Earthlink Postmaster pages Send email to fblrequest@abuse.earthlink.net does not offer Blocked users
Excite Postmaster pages FBL Signup does not offer does not offer
Fastmail FBL Signup
GMX mail.com
Gmail bulk senders guidelines FBL Signup for ESPs does not offer Troubleshooting
Hotmail (Outlook) Hotmail
Integra does not offer does not offer does not offer
Juno United Online
Live.com (Outlook) Hotmail
Mail.com Postmaster page does not offer does not offer Contact Form
Mail.ru Postmaster.mail.ru FBL Signup
Netzero United Online
Office365 Technet
OpenSRS Tucows
Outlook Postmaster Website JMRPP Signup does not offer Outlook support pages
QQ Postmaster pages does not offer does not offer
Rackspace emailsrvr.com FBL Signup does not offer postmaster@emailsrvr.com
Roadrunner Postmaster pages FBL Signup does not offer Support Request Page
Synacor FBL Signup
Terra.com.br FBL Signup
Time Warner Cable RoadRunner
Tucows does not offer FBL Signup does not offer does not offer
United Online Postmaster pages does not offer Whitelist Signup Unblocking Form
Usa.net Postmaster website FBL Signup does not offer IP lookup form
Verizon does not offer Whitelist Signup does not offer
Yahoo Postmaster Pages FBL Signup Yahoo! Mail Bulk Sender Form Detailed Delivery Advice
Postmaster Help
Zoho FBL Signup

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 Note that the “does not publish” for limits means that the ISP has said they have limits, but they do not publish those limits specifically.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
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
QQ 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