When your email server gets blocked by AT&T's mail relay (sbc:blacklist.mailrelay.att.net), you'll typically receive a bounce message like this:

<████████@att.net>: host scc-mailrelay.att.net[204.127.208.75] said:
    521-88.208.246.34 blocked by sbc:blacklist.mailrelay.att.net. 521 DNSRBL:
    Blocked for abuse. See http://att.net/blocks (in reply to MAIL FROM
    command)

First step is to verify your IP's status across multiple DNSBL services. Here's a Python script to check various blacklists:

import dns.resolver

def check_rbl(ip, rbl_domain):
    reversed_ip = '.'.join(reversed(ip.split('.')))
    query = f"{reversed_ip}.{rbl_domain}"
    try:
        answers = dns.resolver.resolve(query, 'A')
        return True, [str(r) for r in answers]
    except:
        return False, None

ip_address = "88.208.246.34"
rbl_services = [
    "blacklist.mailrelay.att.net",
    "bl.spamcop.net",
    "zen.spamhaus.org",
    "b.barracudacentral.org"
]

for rbl in rbl_services:
    listed, details = check_rbl(ip_address, rbl)
    print(f"{rbl}: {'Listed' if listed else 'Not listed'} {details if listed else ''}")

Common reasons for AT&T blacklisting include:

• Spam complaints from AT&T users
• Sudden increase in email volume
• Poor sender reputation score
• Presence in third-party blocklists that AT&T references

Here's the complete remediation workflow:

1. Verify your server isn't an open relay:
   telnet your.mail.server 25
   EHLO test.com
   MAIL FROM: <test@example.com>
   RCPT TO: <external@domain.com>

2. Check your SPF, DKIM, and DMARC records:
   dig TXT yourdomain.com
   dig TXT _dmarc.yourdomain.com
   dig TXT selector._domainkey.yourdomain.com

3. Review your mail server logs for patterns:
   grep "88.208.246.34" /var/log/mail.log | grep "Reject" -B5 -A5

When automated checks don't reveal the issue, you'll need to contact AT&T's postmaster team. Include:

• Your server IP and domain
• Sample message headers that were blocked
• Any relevant log excerpts
• Steps you've taken to resolve the issue

Implement ongoing monitoring with this Bash script:

#!/bin/bash

IP="88.208.246.34"
TEST_EMAIL="test@yourdomain.com"
ATT_RECIPIENT="monitoring@att.net"

while true; do
    echo "Sending test email to AT&T..."
    (
        echo "Subject: AT&T Deliverability Test"
        echo "From: $TEST_EMAIL"
        echo "To: $ATT_RECIPIENT"
        echo ""
        echo "This is an automated deliverability test"
    ) | sendmail -f $TEST_EMAIL $ATT_RECIPIENT
    
    sleep 86400 # 24 hours
done

When your email server gets blocked by AT&T's MailRelay system, you'll typically receive a bounce message like this:

<████████@att.net>: host scc-mailrelay.att.net[204.127.208.75] said:
    521-88.208.246.34 blocked by sbc:blacklist.mailrelay.att.net. 521 DNSRBL:
    Blocked for abuse. See http://att.net/blocks (in reply to MAIL FROM
    command)

From my experience troubleshooting these issues, here are the most frequent causes:

• Spam complaints from AT&T users
• Sudden increase in email volume
• Poor sender reputation (low Sender Score)
• Being listed on third-party RBLs that AT&T references
• Incorrect SPF/DKIM/DMARC configuration

First, verify your IP's status across multiple blacklists:

# Check multiple DNSBLs
dig +short 88.208.246.34.zen.spamhaus.org
dig +short 34.246.208.88.bl.spamcop.net
dig +short 34.246.208.88.ubl.unsubscore.com

For AT&T-specific checks:

# Check AT&T's internal blacklist
dig +short 34.246.208.88.blacklist.mailrelay.att.net

Search your mail logs for patterns around the time of blacklisting:

# Example Postfix log search
grep "88.208.246.34" /var/log/mail.log | grep -i "reject"
grep "att.net" /var/log/mail.log | grep -i "fail"

If you've confirmed it's not a widespread RBL issue:

1. Submit a delisting request through AT&T's official form
2. Implement these Postfix configuration changes to improve reputation:

# /etc/postfix/main.cf
smtpd_recipient_restrictions = 
    permit_mynetworks,
    permit_sasl_authenticated,
    reject_unauth_destination,
    reject_rbl_client zen.spamhaus.org,
    reject_rbl_client bl.spamcop.net,
    check_policy_service unix:private/policy,
    permit

Set up proactive monitoring with this Python script:

import dns.resolver

BLACKLISTS = [
    "zen.spamhaus.org",
    "bl.spamcop.net",
    "blacklist.mailrelay.att.net"
]

def check_blacklist(ip):
    reversed_ip = ".".join(reversed(ip.split(".")))
    for bl in BLACKLISTS:
        try:
            query = f"{reversed_ip}.{bl}"
            answers = dns.resolver.resolve(query, "A")
            print(f"WARNING: {ip} is listed in {bl}")
        except dns.resolver.NXDOMAIN:
            print(f"{ip} not in {bl}")
        except Exception as e:
            print(f"Error checking {bl}: {e}")

check_blacklist("88.208.246.34")