Why are my emails bouncing specifically from Optonline and other ISPs?
Summary
What email marketers say10Marketer opinions
Email marketer from ZeroBounce describes sending relevant, engaging content to your subscribers. Emails that are perceived as spam or unwanted are more likely to result in bounces and blocks.
Email marketer from Email Geeks confirms they had a similar issue with optonline related to Cloudmark.
Email marketer from Email on Acid explains that monitoring sender reputation using tools like Sender Score and Google Postmaster Tools helps identify issues that could be causing bounces from specific ISPs.
Email marketer from GlockApps shares that smaller ISPs like Optonline sometimes have stricter filtering rules or less sophisticated infrastructure, leading to more frequent bounces based on content or reputation triggers.
Email marketer from Reddit mentions a sudden increase in bounces could indicate a compromised sending server, changes in ISP filtering policies, or a spike in spam complaints.
Email marketer from Mailjet explains that bounces from ISPs can be due to spam-like content, poor sender reputation, or being blacklisted.
Email marketer from SendGrid explains removing inactive subscribers from the email list reduces bounce rates and helps maintain sender reputation with ISPs.
Email marketer from MailerQ describes that If your DNS records are not set up correctly, such as missing or incorrect SPF, DKIM, or DMARC records, ISPs may reject your emails.
Email marketer from Litmus recommends gradually increasing sending volume (IP warming) to establish a positive reputation with ISPs, particularly when using a new IP address.
Email marketer from StackOverflow discusses that investigating the specific bounce codes provided by the ISP is crucial for diagnosing the issue (e.g., greylisting, temporary failure, blocked sender).
What the experts say8Expert opinions
Expert from Email Geeks, following up on Kent McGovern's initial suggestion, shares that Cloudmark is a filtering company/reputation provider used by many mid-size ISPs. Poor reputation with Cloudmark can lead to delivery issues at places that use them.
Expert from Email Geeks explains that if your mail is being rejected by an ISP they'll usually do so with a message that suggests why, often with clear reasons.
Expert from Email Geeks mentions that eDataSource will show data from Cloudmark, including spamtrap hits.
Expert from SpamResource explains that maintaining a good reputation is key to avoiding bounces; damage to your reputation can make ISPs more likely to reject your emails.
Expert from Email Geeks says that if the issues are centered around cable providers, it's more likely a response to something specific. Also, advises that DMARC reports can help identify authentication issues.
Expert from Email Geeks explains that validation has a minimal positive effect on Cloudmark reputation. Factors like user engagement (users asking for your mail) and recipient complaints weigh much higher.
Expert from SpamResource explains that if you're seeing bounces specifically from AOL/Verizon (which owns Optonline), it could be related to DMARC policies if you aren't properly authenticated, or because of content or reputation issues causing them to reject your messages.
Expert from Word to the Wise shares that bounces from specific ISPs may be due to your IP address being blacklisted on their internal or third-party blocklists.
What the documentation says4Technical articles
Documentation from RFC Editor details the underlying SMTP protocol which dictates that bounces occur due to issues like invalid recipient addresses, policy rejections by the receiving server, or temporary unavailability of the server. Specific error codes provide further detail.
Documentation from Microsoft details if you exceed your sending limits or send emails to too many invalid recipients, ISPs might block or throttle your emails.
Documentation from Spamhaus explains that being listed on a blocklist (like Spamhaus) will cause widespread rejections and bounces from ISPs that use their data to filter spam.
Documentation from Google suggests that following authentication best practices (SPF, DKIM, DMARC), maintaining a low spam complaint rate, and providing easy unsubscribe options will improve deliverability and reduce bounces.