Why are email complaint rates and bounce issues suddenly increasing with Microsoft (Outlook, Hotmail)?

Marketer from Email Geeks reports that their Microsoft FBL volumes for the past 7 days are between 1.4x and 2.3x normal rates, vs. 30 day averages, depending on the day; with a weekly average of 1.9x.

Email marketer from Mailjet shares that increased bounce rates can be caused by outdated email lists, spam traps, or sudden spikes in email volume which cause you to exceed your sending limits.

Marketer from Email Geeks observed spikes in complaint counts for certain accounts last month, on specific days (19th-20th and 30th-31st), with no significant changes to lists, segmentation, or content. The increase was up to 100x vs. normal complaint levels, and only affected Microsoft domains.

Marketer from Email Geeks shares that their inbound Microsoft FBL volume (unique complaints) jumped significantly beginning on the 11th and has continued at elevated rates since then, also with no changes and with unchanged complaint volume from other FBLs e.g. Yahoo!

Email marketer from Microsoft Support explains that bounce issues on Outlook.com can stem from various causes including exceeding sending limits, having a poor IP/domain reputation, triggering spam filters, or experiencing network issues. They advise checking the sender's reputation via Sender Score or similar services and ensuring compliance with Outlook.com's policies.

Email marketer from Reddit shares that recent changes in Hotmail's spam filtering algorithms may be causing legitimate emails to be marked as spam or bounced. It recommends checking IP reputation and ensuring proper email authentication.

Email marketer from Stack Overflow responds that Hotmail is very strict regarding spam control. Factors impacting deliverability can include IP address blacklisting, missing SPF records, and content triggering spam filters.

Marketer from Email Geeks mentions experiencing major bounce issues with Outlook and Hotmail this week, with deliverability dropping from above 99% to under 90% using the same lists.

Email marketer from SocketLabs shares that ramping up your sending volume slowly over time is important, known as IP Warmup. This helps establish a positive sending reputation with mailbox providers and prevent being flagged as a spammer.

Email marketer from Postmark shares that managing a suppression list is key for maintaining a healthy sender reputation. Including users who unsubscribed or marked emails as spam prevents sending to disengaged addresses and improves deliverability.

Email marketer from Return Path shares that sender reputation is influenced by factors such as email volume, complaint rates, spam trap hits, and the consistency of sending practices. Any sudden changes in these factors can lead to deliverability issues.

Email marketer from Gmass shares that consistently ending up in the spam folder can be a sign of underlying problems, such as a blacklisted IP address or poor sending practices. Sudden changes in inbox placement may suggest recent algorithmic updates.

Email marketer from Email on Acid suggests strategies for repairing a damaged sender reputation, including identifying and removing problematic addresses, improving list hygiene, warming up IPs, and setting up feedback loops.

Email marketer from Litmus says Microsoft and other mailbox providers use engagement metrics (opens, clicks, complaints) to determine sender reputation. Decreased engagement can negatively impact deliverability.

Expert from Spamresource.com explains that a primary factor in Hotmail/Outlook deliverability is sender reputation, which is heavily influenced by complaint rates. A sudden spike in complaints can severely impact deliverability, even for legitimate senders. Other factors include authentication (SPF, DKIM, DMARC), list hygiene, and engagement rates.

Expert from Wordtothewise.com explains the importance of closely managing complaint feedback loops (FBLs) to understand and address issues causing increased complaint rates. Regularly monitoring and reacting to FBL data helps identify problems like list quality issues, content concerns, or authentication failures that can trigger user complaints, directly affecting deliverability at Microsoft and other providers.

Documentation from RFC explains that a properly configured SPF record authorizes which mail servers are allowed to send emails on behalf of your domain. This helps prevent spoofing and phishing, improving deliverability.

Documentation from SparkPost explains that hard bounces indicate a permanent reason for email delivery failure (e.g., invalid email address), while soft bounces are temporary (e.g., full inbox). A sudden increase in hard bounces suggests issues with list hygiene or data quality.

Documentation from Microsoft explains that maintaining a good sender reputation is critical for deliverability to Outlook.com/Hotmail. Sudden increases in complaints can negatively impact reputation, leading to increased bounces. Microsoft recommends monitoring your Sender Reputation Data page in the Microsoft 365 Defender portal.

Documentation from Microsoft emphasizes the importance of authentication (SPF, DKIM, DMARC) for ensuring emails are delivered to the inbox. Incorrect or missing authentication records can lead to deliverability issues and increased bounce rates.