Clarification on Email Warming and Blacklisting: What Actually Gets Affected?

Hi everyone,

I have a couple of questions about email warming and blacklisting that I hope someone can clarify:

When we talk about "warming up emails," what exactly are we warming up? Is it the reputation of my domain, my email server's IP address, or both?
Similarly, when an email sender gets blacklisted, what gets blacklisted? Is it the domain, the server IP, or could it be both?
I'm trying to better understand how these processes work to ensure good email deliverability. Any insights or advice would be greatly appreciated!

Thanks

See, SMTP and Domain are both different. If the domain is blacklisted, sometimes SMTP is still good. If SMTP is blacklisted, the domain is still good.

The warmup concept is mainly done on the domain, but some small receivers need a reputation on both SMTP and the domain. However, the majority of your reputation is held on the domain, so in the future, when you change email marketing services, your reputation will remain on the domain.

Note: Reputation can reset when you keep the domain longer without sending any emails.

Good Luck

Usually it's sender email + IP combination

Thank you for making it clear to me. So, If I want to send bulk email, I should keep 10-15 domain ready. Besides, 2-3 extra vps server in warmup.
Currently I am using contabo vps+aapanel mail server+ mautic.
is that a good idea?

xcodes said:

See, SMTP and Domain are both different. If the domain is blacklisted, sometimes SMTP is still good. If SMTP is blacklisted, the domain is still good.

The warmup concept is mainly done on the domain, but some small receivers need a reputation on both SMTP and the domain. However, the majority of your reputation is held on the domain, so in the future, when you change email marketing services, your reputation will remain on the domain.

Note: Reputation can reset when you keep the domain longer without sending any emails.

Good Luck

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rasel98 said:

is that a good idea?

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Yes, but the limits for fresh domain/ip are low.

vint said:

Yes, but the limits for fresh domain/ip are low.

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Could you please elaborate? I am bit new in this field. I want to keep in warm up additional server and domain, while sending mail with already warmed up. When one get blacklisted I will use other one.

rasel98 said:

When we talk about "warming up emails," what exactly are we warming up? Is it the reputation of my domain, my email server's IP address, or both?

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Usually with warming up people refer to getting Gmail and Hotmail to accept their emails. If your list would be majority not Gmail and not Hotmail, warming up (ie. by buying a warming up service) would make no sense as they usually only warm up for Gmail/Hotmail/Yahoo and maybe Gmx.

You can't warm up an IP or domain "generally" and warminug up has nothing to do with getting publicly blacklisted. You get blacklisted because of sending an email to a spamtrap or user reports (Spamcop).

rasel98 said:

Similarly, when an email sender gets blacklisted, what gets blacklisted? Is it the domain, the server IP, or could it be both?

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You can get your domain publicly blacklisted (major impact blacklists for domains are Spamhaus DBL, SURBL, URIBL) or secretly blacklisted by the server you are sending to. Your IP exactly the same, either publicly blacklisted (major impact for IPs is Spamhaus and Spamcop and to a lesser degree Barracuda ) or the server you are sending to will blacklist you internally, if you f. ex. send too much spam.

Most "generic" email providers like f. ex. Namecheap use public blacklists like Spamhaus to classify your email which means you just don't have to be on it to get your emai laccepted.

What most people miss is — warming up is not some magic fix. You're mainly warming the domain's reputation with major inbox providers (Gmail, Outlook, Yahoo). The IP matters, but in 2025, domain reputation carries more weight long term — especially if you're using shared IPs or rotating pools.

Contabo + aaPanel + Mautic, these are decent for starting out, but Contabo IPs are already on the radar for a lot of ESPs. Don’t expect clean delivery if you're pushing volume. Also, just rotating between 10–15 domains and a few VPS won’t help if you’re reusing the same content, headers, or sending patterns. Smart filters catch that fast.

And getting blacklisted isn’t always about spammy behavior. One bad list, one hidden spamtrap, and you're done. Warmup doesn’t protect you from that. Build slow, monitor each sending pool separately, and never rely on warmup tools blindly, they’re training wheels, not immunity.

LilyRussell said:

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The use of the symbol is always a sure sign of... well, you know.

LilyRussell said:

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Yeah at this point it isn't even trying. Look up dialectical hedging. Easy giveaway.

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Warming up gradually builds the reputation of both your sending domain and IP address, while blacklisting can affect either or both, so managing both carefully is key to maintaining strong email deliverability.