What could cause email timeouts specifically with Comcast/Xfinity?

Email marketer from Reddit notes Xfinity's email policies can be strict, resulting in timeouts if sending patterns trigger spam filters, especially from new IPs or domains. They suggest warming up new IPs and domains gradually.

Email marketer from Email on Acid notes that deliverability issues (potentially manifesting as timeouts) can arise from blacklisting, poor sender reputation, or authentication problems (SPF, DKIM, DMARC). They suggest monitoring sender reputation, authenticating emails, and avoiding spam triggers.

Email marketer from Email Geeks shares that the issues started late Sunday night into Monday morning.

Email marketer from Email Geeks clarifies that nothing is bouncing, but larger queues are dissipating much slower than normal, with consistent timeout messages instead of "Try again later." The MXToolbox test suggests a potentially larger issue.

Email marketer from Email Marketing Forum explains that greylisting, a technique used by some email providers (including Comcast/Xfinity) to combat spam, can cause temporary delays and timeouts for initial email attempts. They recommend configuring sending servers to retry sending emails after a delay.

Email marketer from Email Geeks explains that they've been seeing timeouts to Comcast/Xfinity over the last 24-36 hours. Mail seems to be getting through, but much slower than normal, with timed-out statuses instead of normal replies. MX lookup and SMTP tests from MXToolbox are also inconsistent with "Unable to connect after 15 seconds."

Email marketer from Quora shares that issues with the SMTP server configuration (e.g., incorrect hostname, port number, or authentication settings) can lead to timeouts. They suggest verifying the SMTP settings and ensuring they match the provider's requirements.

Email marketer from Reddit shares that Comcast/Xfinity might be implementing stricter filtering policies, leading to timeouts if the sending server's reputation is questionable or if the email content triggers spam filters. They suggest checking sender reputation and ensuring emails comply with best practices.

Email marketer from Web Hosting Talk mentions that DNS resolution problems can sometimes cause connection timeouts. They advise ensuring that DNS records are correctly configured and that the DNS server is responsive.

Email marketer from StackOverflow explains that slow email delivery, potentially leading to timeouts, could be caused by greylisting (temporary rejection of emails from unknown senders), content filtering delays, or the recipient server's processing capacity. He recommends implementing retry mechanisms and monitoring queue lengths.

Email marketer from Experts Exchange suggests Comcast may be blocking emails due to the sender's IP address being on a blacklist or due to exceeding Comcast's sending limits. They recommend checking if the IP is blacklisted and adhering to Comcast's sending policies.

Expert from Word to the Wise (Laura Atkins) explains that Comcast/Xfinity heavily relies on sender reputation and engagement metrics. Poor sender reputation, low engagement, or sending patterns that appear suspicious can lead to timeouts or deferred delivery.

Expert from Spamresource shares Xfinity are known to use aggressive techniques that are not always technically correct to block emails. Their users also appear to often mis-configure their email programs which leads to difficulty diagnosing real issues.

Documentation from Postfix details various SMTP timeout parameters that can be configured on a Postfix server, which can affect email delivery. These timeouts can range from connection timeouts to data transfer timeouts.

Documentation from MXToolbox describes SMTP connection timeouts as potentially caused by firewall restrictions, incorrect DNS settings, or server downtime on either the sending or receiving end. They recommend verifying DNS records, checking firewall configurations, and confirming server availability.

Documentation from RFC 5321 specifies that SMTP servers can impose timeouts for various stages of the email transmission process. These timeouts are intended to prevent resource exhaustion due to unresponsive clients or network issues. These can cause timeouts if the email is taking too long to send.

Documentation from DNS Records explains that if a DNS server fails to respond in time, it can result in a connection timeout. This means the client (e.g., email server) was unable to resolve the domain name to an IP address within the given timeframe, thus failing to establish a connection.

Documentation from Comcast Support explains that timeouts can occur due to network congestion, server maintenance, or issues with the recipient's email server. They recommend checking the connection, ensuring the server settings are correct, and trying again later.

Documentation from Microsoft explains that Exchange Online Protection (EOP) may reject connections or cause timeouts if the sending server exhibits suspicious behavior or fails to meet EOP's security requirements. They recommend following Microsoft's guidelines for sending emails to Exchange Online.