Struggling with Office 365 Email Deliverability Issues

Jake B. · 2025-04-08 22:20:44.290039+00

Anyone having very bad deliverability to Office 365 mailboxes? It seems as that even personalization, constant warm up with MailReach, and spam testing on their software isn't producing great results. All of my email accounts are healthy and the domains are all trusted and set up through reputable domain providers such as Network Solutions, but man am I getting absolutely nothing back from Office 365 sequences. It's wild because when I use Clay to enrich and send out my emails manually I get at least 2 meetings booked per day. I don't get it. I may toss the towel on sequencing but part of me really wants to figure this out.

Struggling with Office 365 Email Deliverability Issues | Clay

10 comments

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To improve email deliverability to Office 365 mailboxes when using sequencing, consider these strategies: 1. Separate Microsoft from other providers: Create a different sequence for Office 365 recipients and use very short email copy. 2. Focus on domain and inbox health: This is more crucial than the sequencer you're using. 3. Monitor sender scores and work on improving inbox placement. 4. Learn about key concepts like domain segmentation, IP reputation management, and email throttling. 5. Understand and comply with anti-spam regulations like GDPR and CAN-SPAM. If you continue to face issues, consider reviewing your target lists and offer. Remember, cold email sequencers are just one part of the deliverability puzzle.
Sources: Justin R. | Clay Tips for Improving Email List Quality Without Verifiers | Clay Seeking Help with Email Deliverability Basics | Clay
Jake Brozynski
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Bo (Clay)
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Hey, You’re definitely not alone—there’s been a lot of talk lately about poor deliverability to Office 365 mailboxes. Even with warm-up tools, personalization, and proper setup, results have still been inconsistent. I’d recommend checking in with the Smartlead community on Slack—others have been sharing similar issues there, and you might find more insight or workarounds that are working for them. Let me know if you want help testing different setups too.
Jake Brozynski
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Hi Bo, thanks for getting back to me. How do I access the Smartlead community on Slack? Also what different setups could you help me test?
Bo (Clay)
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Hey! You can join the Smartlead community on Slack here: https://join.slack.com/t/smartlead-hq/shared_invite/zt-1iy4gcp45-EPv4ng85bhnK_2yx7ZxTUQ
In Clay, we don't actually send emails, so we can't assist with that aspect. What you can test are different email setups with various email providers.
Regarding your Office 365 deliverability issues, here are some additional tips: 1. Try using different sending patterns - avoid sending in large batches 2. Implement longer delays between emails to appear more natural 3. Consider using separate domains for different campaigns 4. Test different email formats (HTML vs plain text) as Office 365 can be sensitive to heavily formatted emails 5. Experiment with different subject line styles - avoid sales-y terminology 6. Since your manual emails are working, try to closely replicate those exact sending patterns in your sequences 7. Check if your IP is on any blacklists, as this can affect deliverability specifically to Microsoft domains The significant difference between your manual success and automated failure suggests it might be something in the sending pattern that Office 365 is detecting as automated.
Jake Brozynski
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This is great information, thank you! Regarding number 4 what would be considered HTML versus plain text? Aren’t all emails sent using plain text? I guess how can I tell if my email sequences are using plain text versus HTML?
Bo (Clay)
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Plain text emails contain only text with no formatting, while HTML emails include formatting like bold text, colors, images, or hyperlinks. You can tell which type you're using by: 1. Looking at your email composition interface - most platforms have toggles between HTML/rich text and plain text modes 2. Checking if your emails contain any formatting, links with anchor text, or images 3. Looking at the source code of your email templates (many platforms let you view this) Plain text emails typically have higher deliverability to Office 365 because they look more like personal emails. If your sequences include logos, formatted signatures, colorful buttons, or even just bolded text, they're using HTML. Try creating a sequence with absolutely no formatting - just like you'd type in a regular email to a friend - and see if that improves your deliverability.
Jake Brozynski
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Okay I’ll try that. I also didn’t have an opt out link before in my emails so I now just added that. The opt out link is the only link I have in my emails.
Bo (Clay)
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Good luck!!! :)
Channeled
APP
·
·

Channeled
APP
·
·
To improve email deliverability to Office 365 mailboxes when using sequencing, consider these strategies: 1. Separate Microsoft from other providers: Create a different sequence for Office 365 recipients and use very short email copy. 2. Focus on domain and inbox health: This is more crucial than the sequencer you're using. 3. Monitor sender scores and work on improving inbox placement. 4. Learn about key concepts like domain segmentation, IP reputation management, and email throttling. 5. Understand and comply with anti-spam regulations like GDPR and CAN-SPAM. If you continue to face issues, consider reviewing your target lists and offer. Remember, cold email sequencers are just one part of the deliverability puzzle.
Sources: Justin R. | Clay Tips for Improving Email List Quality Without Verifiers | Clay Seeking Help with Email Deliverability Basics | Clay
Jake Brozynski
·
·
no
Bo (Clay)
·
·
Hey, You’re definitely not alone—there’s been a lot of talk lately about poor deliverability to Office 365 mailboxes. Even with warm-up tools, personalization, and proper setup, results have still been inconsistent. I’d recommend checking in with the Smartlead community on Slack—others have been sharing similar issues there, and you might find more insight or workarounds that are working for them. Let me know if you want help testing different setups too.
Jake Brozynski
·
·
Hi Bo, thanks for getting back to me. How do I access the Smartlead community on Slack? Also what different setups could you help me test?
Bo (Clay)
·
·
Hey! You can join the Smartlead community on Slack here: https://join.slack.com/t/smartlead-hq/shared_invite/zt-1iy4gcp45-EPv4ng85bhnK_2yx7ZxTUQ
In Clay, we don't actually send emails, so we can't assist with that aspect. What you can test are different email setups with various email providers.
Regarding your Office 365 deliverability issues, here are some additional tips: 1. Try using different sending patterns - avoid sending in large batches 2. Implement longer delays between emails to appear more natural 3. Consider using separate domains for different campaigns 4. Test different email formats (HTML vs plain text) as Office 365 can be sensitive to heavily formatted emails 5. Experiment with different subject line styles - avoid sales-y terminology 6. Since your manual emails are working, try to closely replicate those exact sending patterns in your sequences 7. Check if your IP is on any blacklists, as this can affect deliverability specifically to Microsoft domains The significant difference between your manual success and automated failure suggests it might be something in the sending pattern that Office 365 is detecting as automated.
Jake Brozynski
·
·
This is great information, thank you! Regarding number 4 what would be considered HTML versus plain text? Aren’t all emails sent using plain text? I guess how can I tell if my email sequences are using plain text versus HTML?
Bo (Clay)
·
·
Plain text emails contain only text with no formatting, while HTML emails include formatting like bold text, colors, images, or hyperlinks. You can tell which type you're using by: 1. Looking at your email composition interface - most platforms have toggles between HTML/rich text and plain text modes 2. Checking if your emails contain any formatting, links with anchor text, or images 3. Looking at the source code of your email templates (many platforms let you view this) Plain text emails typically have higher deliverability to Office 365 because they look more like personal emails. If your sequences include logos, formatted signatures, colorful buttons, or even just bolded text, they're using HTML. Try creating a sequence with absolutely no formatting - just like you'd type in a regular email to a friend - and see if that improves your deliverability.
Jake Brozynski
·
·
Okay I’ll try that. I also didn’t have an opt out link before in my emails so I now just added that. The opt out link is the only link I have in my emails.
Bo (Clay)
·
·
Good luck!!! :)
Channeled
APP
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