150: Email Deliverability Updates for 2026

Welcome back to the Practical Prospecting newsletter!

Email deliverability has changed a lot this year and it’s only getting harder to land in the inbox. But that’s not necessarily a bad thing.

Yes, it’s more complex now avoid spam. But the more complex things get, the more people will give up on cold email entirely, leaving room for people like you and I who are willing to go the extra mile.

I wouldn’t call myself the #1 expert on this topic, but we manage thousands of inboxes for clients across many industries, so we end up testing more of this stuff than most.

In this newsletter I’ll share what’s changed, what I’m still unsure about, and what our new process looks like today.

Agenda:

• 9 Email Deliverability Changes & Tips

• Our Recommended Setup for 2026

1. Domain forwarding might be doing the opposite of what you think

For years I assumed forwarding your alt domains back to your main domain was just good practice.

What I'm hearing now is that Google and Outlook can actually flag that. A bunch of domains all forwarding to the same root domain is a pattern, and patterns get flagged. Instead of protecting your main domain, you might be giving ESPs an easy way to tie everything together and burn the whole group of domains faster.

I don't think this is settled yet. But it's flipped enough for me that I'm not forwarding domains by default anymore.

2. ESP matching probably isn't doing much

This one is still up for debate. Some people swear that matching your ESP to the recipients ESP (i.e. Gmail to Gmail and Outlook to Outlook) improves deliverability. And a lot of sending tools, like Smartlead, offer this as a feature now.

But with Gmail specifically, it might be working against you. Gmail has more behavioral data on its own users than any other provider, and there's evidence it actually scrutinizes same-ESP sends harder.

Again, still up for debate. But I turned this off for us, we didn’t see a noticeable difference anyway.

3. Linking your domain to an actual site still helps

Having your alternative domains linked to an actual live site (not forwarded, like we talked about in point #1) is a small trust signal for both mailbox providers and prospects who actually clicks through.

The problem is it’s a big operational lift to create websites for every alternative domain when you have hundreds of them (or thousands… like me).

For people with a small TAM and fewer domains, it might be worth doing. But not the end of the world if you don’t.

It's not required, and it's more operational lift than most people want to take on for a domain they're going to rotate out in a couple months. But if you have the bandwidth, it’s probably worth it.

4. Regularly replacing infrastructure is a must

One of the biggest things we try to focus on as a cold email agency is eliminating “wasted volume”.

Meaning, if we’re sending out emails from inboxes that are damaged or totally burned, we’re wasting valuable sends. So we should be replacing those inboxes with fresh ones ASAP.

The truth is, there’s no definitive way to know when an inbox is burned. But you can get a pretty good idea by looking at 3 metrics:

1. Warmup Score

   1. Most email sending tools (Smartlead, Instantly, etc.) give you this metric. Warmup score is based on how many of your warmup emails ended up in spam vs the inbox. If it’s below 90%, it’s usually a good indicator that your mailboxes are starting to burn.

2. Bounce Rate

   1. If your inbox has had a bounce rate 3% with meaningful volume (1k+ sends), it might be worth replacing.

3. Reply Rate

   1. If your inbox has a reply rate lower than .3%, or worse, you’re not even getting “Out-of-Office” replies from it, then it’s most likely burned.

We set up a weekly automated system in Claude that flags all inboxes below these thresholds and replaces them with new inboxes (reply to this email if you want the system - happy to share).

Smartlead actually just released a feature for automating this as well. You set your reply rate/bounce rate thresholds, and if your inboxes dip below that, it will automatically replace those inboxes with new ones. It’s in a beta right now but it’s promising so far. .

5. External deliverability checkers are optional, not essential

Tools like Glockapps and many others get talked about a lot. I've never personally used them and haven't run into issues without them. That's not me saying they're useless, plenty of people swear by them. But if you're already watching bounce rate and reply rate closely, you probably don’t need to pay for another tool to do separate spam checks.

6. Rotate infra, don't delete it

One thing that's made a real difference for us: treating infrastructure like it's on a schedule instead of something you set up once and leave alone.

We rotate which domains and inboxes are active every couple weeks instead of running the same set into the ground. That way, each set of inboxes get a 2 week resting period every month. It helps them last longer so we don’t have to keep buying new inboxes so quickly.

7. Segment out secure email gateways before you send

I recommend filtering out contacts in your lists who are on Mimecast, Proofpoint, Barracuda, or similar gateways.

These emails are always the toughest to reach, and if you’re primarily sending to them, you’ll burn your inboxes faster.

Prospeo actually has a feature that lets you filter out the email providers you don’t want to send to:

If you have a big list that you can afford to filter down, I’d recommend only sending to Google and Microsoft. Come back to Proofpoint, Mimecast, and others once you’ve found a message that you know will convert.

8. Keep it plain text and vary your signatures

At this point, I feel like it should go without saying but we still only send entirely plain text emails.

No images, links, etc. and open/click tracking turned off.

On top of that, we’ve removed phone numbers and websites from our email signature as it’s an easy way for ESPs to identify when you’re using the same exact signature across hundreds of emails.

9. The messaging side matters as much as the infra side

People obsess over infra and forget the actual copy is part of the pattern too.

If the same template gets sent at real scale, (10s or hundreds of thousands of emails), it starts getting flagged even if you rotate every piece of infrastructure underneath it.

To avoid this, we refresh our messaging for high volume campaigns once a month. It doesn't need to be a full rewrite, but enough of a change that it's not the exact same pattern hitting inboxes over and over.

I’m in the process of setting up a Claude automation that will do this for me. Ideally it will look at all our high volume, consistent campaigns, and refresh the messaging every 2-4 weeks on it’s own. That hard part is getting it not to change the core of the message that’s actually working. I’ll share this on LinkedIn once I have it done.

Our Recommended Setup

Here's roughly how we set things up when we're standing up new infrastructure for a client.

First, we split across two email inbox providers. If one provider has an outage or a bad week, you're not stuck. Never put all your inboxes with a single vendor.

Then we split by mailbox type too. Google and Microsoft behave differently, get flagged differently, and recover differently, so we run both rather than betting on one.

On the sending caps:

• Google inboxes:

  • max 15 emails a day per inbox

  • max 3 inboxes per domain

• Microsoft inboxes:

  • max 5 emails a day per inbox

  • max 10 inboxes per domain

Notice Microsoft lets you stack way more inboxes per domain but at a much lower daily send. Google is the opposite, fewer inboxes but each one can carry more volume.

We still warmup everything up for at least 2 weeks before sending. But 4 weeks is ideal if you have the runway for it.

On domains, we stick to .co and .com only. We've tested other TLDs and they just don't perform as well.

And if you're buying over 50 domains at once, split the purchase across different providers, different days, or different accounts. Buying 100 domains in one shot from one place is an easy pattern for providers to catch, and all your domains can get flagged before you've sent a single email.

Here’s a list of infrastructure providers that I trust and have used/currently use (in no particular order):

1. ZapMail

2. Hypertide

3. MissionInbox

4. ScaledMail

Thanks for reading,

Jed