Premium Dedicated Email Server [Warmed UP] - 6 Months

Table of Contents

• 1. Background
• 2. What is the situation?
• 3. My firsthand experience
• 4. What these ESPs do to restrict traffic?
• 5. What constitutes Spamming?
• 6. How to avoid being a spammer?
• 7. Mass Mailing Science
• 8. IP Rotation (A big No)

1. Background

I have deployed and configured Mass Mailing Setup 30 times, for more than 15 companies which included multiple Postfix instances, load balanced with HAProxy, for stack details refer to Stack Details.

From my point of view, this whole matter is very subjective in nature and has no single line solution or strategy. You have to continuously monitor, change your strategies and improvise accordingly. In order to address the issue, we must first understand how it all works. What are the ESPs' interests, their limitations? What are senders’ interests and their limitations?

2. What is the situation?

The ESPs own servers and mailboxes, they want to protect their customers from spam and contrary to it, we want to send huge traffic to their networks/servers. Logically they are justified in restricting our access to their networks/servers and stop us from bringing their networks/servers to its knees.

Yes, this is what we do, we send millions and millions of emails (or make connections) to their networks/servers. That is huge traffic and why should they bear so much cost to entertain our huge traffic to their network when we aren’t even paying them anything for that.

That is the game: they want to restrict us, and we want to push in. They have the control, and we have to resort to ways to manipulate their rules.

3. My firsthand experience

1. To start with, before 2015 "No One" (Gmail, Yahoo, Hotmail) bothered about SPF, DMARC, DKIM, rDNS/PTR much, though they did claim on their support pages that it's recommended, but they did accept traffic from your IP leading straight to the inbox.


2. It was Hotmail which started rejecting emails if you did not have a valid PTR/rDNS record after 2015 , while SPF, DMARC, DKIM were still optional back then.


3. Yahoo and Gmail were still okay with that.


4. Yahoo was the only ESP amongst these three that was sharing feedback via a Feedback Loop service which they were offering with the help of Return Path.


5. Yahoo would email you the list of their users who had marked you as a spammer to help you either remove them or request them to mark you safe.


6. Hotmail introduced SNDS after 2015 and Gmail also jumped into the pool after that with Google Postmaster service, back in 2015.


7. Yahoo dropped Return Path and started their own Feedback loop mechanism, so no more sharing of user lists with us.
8. They all started hardening their email network and improving their anti-spam policies. The result is Gmail came up with the worst content filter amongst all these ESPs, called Google Magic unofficially, back in 2017, to the best of my knowledge.

4. What these ESPs do to restrict traffic?

1. They restrict you (mark you as spammer) based on the number of connections that you are making to their networks/servers.
2. They (especially Google) mark you as a spammer on the basis of your content as well.

5. What constitutes Spamming?

SPAM doesn’t only mean that you are sending too many emails, opening too many connections, or sending some adult, wrong, financial, scammy blah blah text or information in your email or to people who have not OPT-IN or DOUBLE OPT-IN to receive emails from you.

SPAM does include the above-mentioned stuff plus, email sent to spam trap accounts, too many bounces, sending at a very high rate from the SAME IP or from the SAME DOMAIN and the SAME CONTENT all over repeatedly. It also includes but is not limited to sudden spikes in sending rate, unusual and unexpected rate of sending, even if your contacts have OPT-IN or DOUBLE OPT-IN.

6. How to avoid being a spammer?

1. Sending at a limited and tailored rate.
2. Ensure your content is tailored accordingly.
3. Gmail uses a magic filter. Fortunately, Yahoo and Hotmail don't till now, but other ESPs do use such content filters which look for the following:
   • Is the same subject being repeated?
   • Is the content the same?
   • Is the same hyperlink being repeated? (Even if you may change the subject, that won’t help you.)
4. Mix and match emails with different subjects, contents, and links.
5. Use a separate domain or at least a separate subdomain for each kind of content/subject.
6. I am not including the technical details here like SPF, DKIM, ADSP, rDNS, DMARC, etc.

7. Mass Mailing Science

Mass mailing is a very complex process and depends on a lot of things and yes, it’s a long, ongoing, and relies on a trial and error basis thing.

The Process:

When a reputable server receives an email, they check the following (brief):

7.1 Criteria 1 - IP Reputation:

• Is your IP blacklisted by SBL, XBL or PBL (collectively known as the 'Zen' block list)?
• SPF - is it from the designated sender?
• DKIM - Whether the message is digitally signed?
• Does a PTR or rDNS exist?
• DMARC being used? (spoof-able?)
• Feedback Loops and resolution?
• Bounce rate management?
• Un-subscribe option available?
• Subject and Email Body standards?

7.2 Criteria 2 – Tailoring the rate of sending - The most complex part:

• The rate at which you are sending.
• The domain that you are sending from.
• The IP that you are sending from.
• IP and domain name go hand in hand, you cannot cheat them by having changing IPs pointing to the same domain, will still reject, especially with Gmail, they block the domain name if they find that you are bombarding via multiple IPs but using the same domain name.
• In the case of Gmail, their new content filter is very strict and they quickly block on the basis of your content.
• Will talk about multiple sub-domain strategy later.

7.3 My Postfix Strategy:

• Postfix can very easily be tailored let me share my current strategy (briefly).
• I create separate rules for each domain like Gmail, Hotmail, Yahoo, and tens of others for not just sending but logging as well.
• It SIMULTANEOUSLY sends to EACH unique destination with different rates (keeps increasing or decreasing based on logs – trial and error).
• Rate is tailored at multiple levels like, individual domain and mailbox per domain.
• Separate From:subdomain for each category.

7.4 Destination wise rules:

Let me define what I mean by destination here:

By destination, I mean, for example, one of my client's lists contained:

• 63,691 business domains hosted with GMAIL + Gmail itself meaning individual@gmail.com users.
• 49,232 business domains hosted with Godaddy.
• 24,394 business domains hosted with Hotmail.
• 8,132 business domains hosted with 1and1.
• 7,622 business domains hosted with BigCommerce.
• 6,174 business domains hosted with EmailSrvr.com.
• 5,790 business domains hosted with Volusion.com.
• 3,434 business domains hosted with MailSpamProtection.com.
• 2,068 business domains hosted with Yahoo.

These are just a few famous ones mentioned for the sake of brevity, there is a long list.

If you think you are making a connection to abc.com, cnx.com or vpn.com and all these are unique destinations then you might be wrong as all these domains may be hosted with Gmail, Hotmail, or Yahoo, so apparently you are sending to abc.com but you are connecting to Gmail servers.

Let’s consider Gmail for example:

All these 63,691 domains plus gmail.com itself will be clubbed into one destination and one transport rule and the sending rate and delay will be added accordingly.

If you happen to send 1 email per minute to Gmail servers that would imply 60 per hour, 1,440 per day, 10,080 per week. 43,200 emails to Gmail Servers, which is considered as bombardment or an attempt to bring their servers to their knees. Remember you are not the only one who wants to send to Gmail, right? So how to tackle this situation?

Well, you keep a slow and constant rate of sending that is acceptable to their servers. You start very slow initially when your IP is cold and keep increasing the rate with the passage of time once your IP has turned its status from Cold to Warm but still, you should never bombard and instead remain limited and add additional number of Servers to scale up.

8. IP Rotation (A big No)

The concept that people have in mind is that since you cannot send too much traffic from one single IP, therefore, you can have multiple IPs that you can rotate after every certain second, doing so can trick the remote servers into believing that the traffic coming from the same IP and hence they won’t blacklist you. But here is the catch:

• The sender domain, the subject, the URLs, and the overall content remain the same. Since IP Rotation is random, most of the time you are using the same IP for the same remote destination, so the concept of IP Rotation fails badly, seems useless, and is not at all practical. The concept of destination has been addressed above already.


• Secondly, mere changing of IP won’t help anymore, especially after 2017, when Google came up with their very strict content filter. They simply block your Domain name, they don’t care. Sometimes they block all emails from your domain, or sometimes they simply block emails with a specific subject, which they find is being repeated.


• Yahoo and Hotmail don’t have such strict content filters, but domains hosted by Godaddy, BigCommerce, 1and1, Volusion, etc. offer anti-spam services too, which are equally strict. Most of these ESPs now use CSI, Cyren, or Barracuda, etc.