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Microsoft wants people with Outlook inboxes to have the best possible user experience.
Unfortunately for lead gen agencies, that means it’s started to aggressively crack down on cold outreach.
But all’s not lost. Read on to learn the ins and outs of how to send bulk email from Outlook in 2025 — including new best practices and how QuickMail can help.
Let’s get into it…
Can You Send Bulk Email From Outlook?
Yes, you can still do mass mailing from Outlook in 2025 — it’s just become a little more challenging.
That’s because Microsoft has started leveraging sender-bounced emails to crack down on cold outreach.
What Are Sender-Bounced Emails?
For the uninitiated, sender-bounced emails are when your email service provider (in this case, Outlook) prevents your email from being delivered.
However, they’re kinda sneaky about it.
Rather than telling you upfront that an email can’t (or won’t) be sent, the ESP sends you a bounce notification down the line informing you that they chose not to deliver your email — even if the email address was valid.
With many software systems, this looks exactly the same as a “classic” email bounce, when you try sending to an invalid address on your contact list.
Our data for all emails sent with Microsoft 365 (Outlook) on QuickMail suggests that Microsoft began seriously flexing its muscles with sender-bounced emails in summer 2024. Take a look at the big spike in bounces in mid-July:
Bounce rates through our cold email software are typically low because we give all our customers a “light debounce”, which automatically stops them from sending to domains that:
Don’t exist
Don’t have an associated email service
When we first spotted that surge in bounces on our email platform, we assumed Microsoft had screwed something up on its side.
But when it happened again — albeit to a lesser extent — in September, it became clear that this was no mistake.
(Also, you might have noticed that our screenshot shows another small increase in bounces in May. In hindsight, we now think Microsoft was testing the waters with a limited number of accounts, before rolling out a universal update a couple months later.)
To learn more, check out our founder Jeremy’s discussion with SalesBread CEO Jack Reamer on Microsoft deliverability:
How to Send Bulk Emails in Outlook: 5 Key Actions
So if Microsoft’s aggressive use of sender-bounced emails is here to stay, should we all just pack up and go home?
Of course not — it’s just a case of accepting that the landscape has changed and updating our processes.
With that in mind, here are five simple steps you should take right now to give yourself the best chance of sending bulk messages in Outlook while maintaining a low bounce rate:
1. Avoid Sudden Changes in Sending Volume
Sure, you want to scale your bulk email campaigns as quickly as possible.
But going from zero to 100 real quick will likely set alarm bells ringing at Microsoft’s end.
This best practice applies to any ESP. But whereas other providers — like Gmail — will just send your emails to the spam folder, Microsoft will refuse to send them altogether.
Pro tip: Don’t forget that auto warmer sends are just like any other email sent through Outlook. So if you instantly go from 10 auto warmer sends a day to 100, there’s a good chance you’ll start seeing more sender-bounced emails.
2. Increase Delays Between Emails Going Out
Sending high volumes of emails in a short space of time is a good indication that you’re running bulk cold email campaigns, so it’s best avoided.
Instead, spread your emails throughout the day — and stick to natural-looking sending times rather than sending 24/7.
3. Write Lots of Email Variants
Another surefire way to attract Microsoft’s attention is to send the same email message, over and over again, with only a couple minor changes (like the email recipient’s name and/or company name).
To tackle this, you can either limit yourself to only sending one or two emails a day, which isn’t exactly scalable. Or you can add a high number of variables to every email you send, such as using mail merge and Spintax.
4. Use Custom Domain Tracking
You should use custom domain tracking if you:
Track opens and/or clicks
Use unsubscribe links in your emails
Having custom domain tracking gives you full control over your reputation because you're not sharing the tracking links with other users. Essentially, it puts you in control of your domain's reputation, boosting email deliverability.
5. Cut Down on "Real" Bounces
As well as taking measures to reduce sender-bounced emails, you should strive to stamp out “real” bounces (i.e. those that happen when you send to an invalid email address).
This is more important than ever, because it looks like Microsoft has lowered its tolerance for these bounces too.
So make sure you always take the time to clean and verify your email list before triggering a new email sequence.
Learn more: The Definitive Guide To Prevent Email Bounce
How Does QuickMail Help You Send Mass Emails From Outlook?
As we’ve explained, it’s still perfectly possible to send bulk email from Outlook in 2025, provided you stick to our best practices.
But the last thing you want is to make it harder for your reps to send the same number of emails they were originally sending, because that’ll hurt your results.
Fortunately, it doesn’t have to be like that. Here are three simple ways that QuickMail helps you keep sending volumes high without risking a ton of sender-bounced emails:
1. Auto Sender Bounce Detection and Campaign Pause
In an ideal world, you’ll never encounter a single sender-bounced email.
But if we do detect a sender bounce, we’ll automatically:
Pause your inbox
Notify you by email
That way, you won’t end up with a high volume of “fake” bounces, and you can retarget the leads that bounced at a later point.
2. AI-Powered Email Rewrites
One of QuickMail’s newest additions is Reword with AI.
As the name suggests, it uses AI to automatically rephrase all emails going out, so you never send exactly the same email twice. You can activate this feature for every email step in your mass email blasts:
When all your emails are unique, it’s harder for them to be flagged as spam (or sender-bounced emails).
3. Add a Minimum Delay Interval Between Email Sends
We’ve already noted that sending a constant stream of cold emails, one after the other, is a bad move if you want to keep your bounce rate low.
That’s why we make it easy to add delays between each individual message.
All you have to do is filter for Microsoft email addresses in QuickMail…
…then select all your Microsoft addresses and set a minimum delay of 10 minutes between emails:
Optionally, you can also add an additional random time variation between emails, up to a maximum length of your choosing:
Clearly, adding delays between emails means you’ll be sending fewer emails overall from a given inbox as well as emulating human-like sending, which means your activity looks more trustworthy.
Still, you’re presumably already using inbox rotation to scale your sending anyway — and if you aren’t, you definitely should be.
Every QuickMail agency plan includes unlimited email accounts, so you don’t need to worry about your outreach campaigns becoming unscalable. You can always increase sends by adding more inboxes.
Boost Your Email Deliverability With QuickMail
At QuickMail, we know that high deliverability is critical to the performance of your cold outreach campaigns.
Because the more emails you send that bounce or land in the spam folder, the fewer people will see your messages — which means fewer opens, replies, and leads.
That’s why every QuickMail agency plan includes a whole suite of deliverability-enhancing tools, including:
Free auto warmer access with MailFlow
Unlimited email addresses
Inbox rotation
Variable time delays between emails
Email blacklist monitoring
Plus you get Deliverability AI, our proprietary solution that automatically swaps out low-performing inboxes for higher-rated ones.
Sounds good? Speak to us to learn more.
