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 pages Whitelist Signup AOL support pages
AOL Postmaster Blog
AT&T postmaster pages does not offer does not offer SMTP errors list
Bellsouth postmaster pages does not offer does not offer unblocking page
Charter postmaster pages does not offer does not offer
Comcast postmaster pages Comcast FBL signup page does not offer blocklist removal form
Cox postmaster pages Cox FBL signup page does not offer blocklist removal form
Earthlink postmaster site Send email to fblrequest@abuse.earthlink.net does not provide blocked users
Excite postmaster website does provide does not provide does not provide
Fastmail FBL signup
GMX mail.com
Gmail bulk senders guidelines does not provide does not offer troubleshooting
Hotmail Postmaster Website JMRPP signup pages does not provide a whitelist Hotmail support pages
Integra does not offer does not offer does not offer
Juno United Online
Live.com Hotmail
Mail.com postmaster page does not provide does not offer contact form
Mail.ru postmaster.mail.ru FBL Signup
Netzero United Online
OpenSRS Tucows
Outlook Hotmail
QQ postmaster pages does not provide does not provide
Rackspace emailsrvr.com Rackspace FBL signup page does not offer postmaster@emailsrvr.com
Roadrunner postmaster site FBL page no whitelist provided contact
Synacor feedback loop
Terra.com.br FBL Signup
Time Warner Cable RoadRunner
Tucows does not provide Tucows FBL signup page does not offer does not provide
United Online postmaster pages does not provide whitelist application unblocking form
Usa.net postmaster website does provide does not provide IP lookup form
Verizon does not provide whitelist does not provide
Yahoo Postmaster Pages Complaint Feedback Loop Yahoo! Mail Bulk Sender Form detailed delivery advice
support request form
Zoho signup link

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 Note that the "does not publish" for limits means that the ISP has said they have limits, but they do not publish those limits specifically.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