What are common causes of email deliverability problems with Outlook.com?

Email marketer from Email Geeks explains it's probably lack of a custom/aligned return path (5321.From) domain with a legitimate source as opposed to something dodgy, and that DMARC is still passing as their DKIM seems to be aligned.

Email marketer from Mailjet explains that poor list hygiene (sending to outdated, inactive, or purchased lists) can lead to high bounce rates and spam complaints, negatively impacting your sender reputation with Outlook.

Email marketer from Email Geeks points out that Microsoft 365 started requiring DMARC recently or it sends to spam, suggesting this as a potential cause.

Email marketer from Reddit user u/mailblaster123 shares that using URL shorteners in your email body is often flagged as suspicious and will cause deliverability issues.

Email marketer from EmailDrips suggests that having a dedicated IP address can help build a positive sending reputation with Outlook, especially if you send a high volume of emails. Sharing an IP address with other senders can be problematic if they engage in poor sending practices.

Email marketer from Email Geeks shares that Microsoft looks at engagement, IP/domain reputation and phases of the moon when filtering email.

Email marketer from Gmass states that Sending emails from a new IP address or domain, especially with high volume, can trigger spam filters. Outlook needs to build trust with your sending source.

Email marketer from EmailVendorSelection.com explains that low engagement (low open rates, click-through rates) is a significant factor. Outlook weighs user engagement heavily, so if recipients aren't interacting with your emails, they're more likely to be filtered as spam.

Email marketer from HubSpot suggests that not having proper email authentication set up, such as SPF, DKIM, and DMARC records, can lead to deliverability issues. These records help verify that your emails are legitimate and not spoofed.

Email marketer from StackExchange user user2987 says to check the content of your email. Using spam trigger words (e.g., "free," "guarantee," excessive exclamation points) can cause Outlook to flag your emails as spam.

Email marketer from Email Geeks asks what type of seed lists are being used, whether home grown, made up (a.k.a. AI powered), etc.

Email marketer from Email Geeks says that deliverability means inbox vs. junk, and delivery means bounce or not, though even those definitions are too vague due to the different kinds of bounce errors.

Email marketer from Email Marketing Forum user JohnS highlights the importance of maintaining a consistent sending volume. Suddenly increasing your sending volume can trigger spam filters.

Email marketer from Litmus shares that ensure your email templates are properly coded and responsive. Poorly coded emails can render incorrectly or trigger spam filters.

Email marketer from Email Geeks asks for clarification on what "deliverability problem" means to the client (no opens, disappearing emails, bounced emails, no sales?) as it can mean different things to different people.

Email marketer from Email Geeks shares not to poke around looking for deliverability problems unless the client expresses a concern and you understand their business model/email marketing activities 100% first.

Expert from Word to the Wise responds by sharing that consistently sending to unengaged users significantly hurts deliverability. Microsoft actively tracks engagement metrics, so targeting inactive or uninterested subscribers leads to increased spam filtering.

Expert from Spam Resource explains that poor sender reputation is a primary cause; Microsoft heavily relies on sender reputation, so a damaged reputation will lead to deliverability issues. This includes IP reputation, domain reputation, and the reputation of your sending practices.

Expert from Word to the Wise explains that high complaint rates are a major factor in Outlook deliverability issues. If a significant percentage of your recipients mark your emails as spam, Microsoft will penalize your sender reputation and filter your emails.

Documentation from Microsoft explains that Sending emails that are considered unsolicited or unwanted by recipients can lead to deliverability issues. This can happen if recipients did not explicitly consent to receive emails from you, or if they have difficulty unsubscribing from your mailing list.

Documentation from Microsoft explains that ensure your sending domain is properly authenticated with SPF, DKIM, and DMARC. This helps Outlook verify that you are authorized to send emails on behalf of your domain.

Documentation from Microsoft responds by stating that being listed on blocklists (also known as real-time blocklists or RBLs) is a common cause. Check if your IP address or domain is on any major blocklists and take steps to get delisted.