Why does email go to inbox? And why not?

"How should I do to not let my emails to spam?" is probably the most frequently asked question about email marketing? Going to the inbox or spam does not depend on your own desire, and there is not always a single answer for it.


Before we talk about why e-mails come to inbox/spam, we need to understand the cause of this situation.

How horrible is a spamming email?

What is a spam email? Surely everyone knows that email is sent to you without your permission. If you have allowed the other party to send it, then it is good or bad may not lie in the category of spam anymore and you can unsubscribe (at any time). But why do we have to give permission to make things to be complicated? Can we just receive all sent emails?

Did you know how many e-mails sent per second? About 2,600,000 are sent per second, equivalent to 156,000,000 per minute, 9,360,000,000 per hour and 224,000,000,000 (In words: two hundred and twenty-four billion) per day.

Of the 224 billion emails, it is estimated that 90% or more are abusive (including unsolicited email and spam). Some security companies, such as Kaspersky and Symantec, estimate the number of spam emails to be between 53% and 58% (of course, people who use anti-virus know their anti-virus habits). In general, the positive view is that only 55% of spam is out of the total 224 billion emails are still 123 billion spam/abusive and when divided to the world population (7.5 billion), every day receive at least 16 emails and nearly 500 spam emails per month.


In addition, Vietnam is the second largest spam-based country in the world, according to Kaspersky Lab, which accounts for about 7.8% of all spam emails worldwide.

Why is the email spamming so terrible? Part of that is because email is a very effective means of transport and at the same time its cost is very low. Spammers can use the software to collect millions of emails and send them without concern or discrimination. Of the millions of emails sent, just a few people buy the product is enough for the spammers to offset the cost of sending. And in the spam e-mail there are more dangerous things than just emails promoting drugs that increase their size or endurance: phishing emails or virus transmission. The fraudulent emails that everyone would have received: a Nigerian prince or a Welsh banker with a fortune and just support (by providing bank account information) would be Divided into a large sum, each year hundreds of thousands of people are fooled with the amount of tens of billions of dollars. The email virus transmission is more dangerous because when you click on the links in the emails, your computer can be installed applications, information gathering (including bank accounts, payment accounts) and at This computer becomes part of the system of bad guys to constantly send more virus emails to others.

A silent war against spam emails

Fortunately, you can now be considered peaceful when the massive amount of spam emails is kept by a giant wall called a spam firewall before it arrives your mailbox.


Spam firewall has multiple layers of protection to detect and combat spam emails:

1. The blacklist list

There are some active neutral parties and build lists that automatically update the IPs and domains that regularly send spam emails. Before the e-mail arrives at your inbox, it usually goes through a checklist of these blacklists (whichever blacklist your email service is using), and this is the step that most spam emails will have. block - about 85% - 90%, spam emails will not even get to your inbox. Spamhaus, SOBS or UCEPROTECT are some common blacklist nowadays.

In addition, some blacklists use a method called honeypot in which they create completely unlinked emails, attach to any service, organizational or personal information, and send emails. This is for public places such as social networking, forums or websites. Because these emails are not subscribed to any email lists, nor are they used, so if any of the parties send email to this address, it's almost certain they have used the tool. To scan the email or email is in the list they buy and whatever the reason, they also violate the rules of spam and now the IPs, the server sends that email will be put into the blacklist.

How Spamhaus works. Source: Spamhaus.
So if you have a situation where your email sent that the client or the other often does not receive, then you sometimes need to review. As far as you may know, there is a chance that your domain or IP of your server has been put on the list of The blacklist system (and actually this is one of the first things you should do). How to check? Most systems allow you to check whether you are in their spam database:
  • https://www.spamhaus.org/lookup/
  • http://www.sorbs.net/lookup.shtml
  • http://www.uceprotect.net/en/rblcheck.php
* You can check by domain website or IP. How to know your IP website? Go to Google and search for "what is my website IP" and try the first few results.

If your website is not on the list, there is nothing to say. But if your IP or domain is on the list it will be a little tired because then it is almost certain that your email delivery rate will be severely affected. Why was this situation happened to you? In the case that you are sure of not offending by buying email lists, then some of the reasons may be due to your hosting shared with multiple people and one of those users is spamming. Otherwise, your computer can be infected with a virus and a part of a spamming system that is controlled by somebody. Or maybe your ISP can blame you for the whole range of blacklisted IPs.
And there is no easy or fast way to deal with it and that will be the case. If it is due to hosting, then you should ask the hosting party to change another IP for yourself and let them know that the IP has problems for them to handle. If you are using your home network, you can inform the network to have solutions. If you think that your computer is infected with a virus, you should scan for viruses, reinstall your PC, or have a specialized office to handle them. But in general, it will be very complicated and no less frustrating for you.

After resolving these issues, you can now apply for blacklist systems to remove your IP or domain from the list, but there is no guarantee they will remove it and do not know when. The last solution is that you may have to remove the domain or IP if you want to continue sending emails. The blacklist system like the famous Spamhaus is causing so many desperate people to do nothing.

2. Filters

No matter how blacklisted the listings are, they will not filter out all spam emails and some will still fall into your inbox and this is where email filters work and break. Divide to decide which email is going to your inbox or junk/spam. The spam filters use a lot of different factors to evaluate and not just because this factor is not met but your email will go to the spam mailbox which will be based on the score. Each factor will have some effect on the score, with little increase factor, factor increase. If your score is above a certain level, your email will default to junk/spam. SpamAssassin, for example, is a fairly well-used filter, and you can get a detailed list of the SpamAssassin Filter (version 3.3x). These factors are divided:

Email content

Email content is the main factor affecting where you email. For example, your email contains adult words such as porn, sex, viagra, each word you will be added 1 point. Free (free) also gets you 1 point. Well, do you know that just having "dear friend" and you get a plus of 2.6 points?

Promising to make a lot of money, 100% guarantee is also the word usually appears in spam emails.
Therefore, you should study word lists which are often badly evaluated thoroughly to avoid (as on the above list). Also, by using our popular logical thinking, we can find some things that should NOT annoy the readers:
  • Use all capitalized words (all caps)
  • Write in bold, whole
  • Use a variety of colors in the text
  • Contains many special characters
  • Use too many images (slow upload speed)
  • Use only 1 image: raw email is a picture
  • Use link shortened (bitly.com, goo.gl)
  • ...

Meta data of email


Include the source names of information from and to. For example, an email information field should have a recipient's name in the email to show that you know the person. The filter will also check if the sender is already in the address list sent previously. What other objects are cc, bcc in email? Also, free-to-email emails like @ gmail.com, @ yahoo.com, @ live.com, etc. will often be underestimated as email coming from authenticated email addresses. But even email with authenticated domain is also up to the previous history to judge. So it's best to keep the customer lists you submit are the right listings and you've emailed them before.

Email's code


An email template as well as a web page, coded primarily by the programming language (mainly HTML / CSS). If the code of the email template is not good, then it will affect. So what can you do?
  • Standardize HTML / CSS, using some tools such as Validator to check for common errors.
  • Does email templates optimize for mobile devices?
  • The ratio between HTML and text in the content (too much code or too much text is not good).
  • Collage content: code from Words (this is why paste from Words)
  • Use different fonts and sizes differently mixed

Bayesian filter

Filter systems such as SpamAssassin use the Bayesian filter as a way of doing things by observing how users use and filter their emails, such as which emails they put in junk/spam, and read them. Then, compare it with other junk/spam emails to compare the similarities in title and content, and then gradually learn how to scan all the emails for a more accurate evaluation.

SpamAssassin with Bayesian filter is a component. Source: JAM Software.
Bayesian poisoning is a term used when spammers using methods such as inserting unused keywords or normal words to make the Bayesian filter misjudge and thereby pass more spam emails. A lot of reports and research have been published on this, but there is no way to completely overcome the Bayesian system.

So how do my emails go into the inbox (more)?

After all, you now understand that emails going to inbox does not depend solely on what tool you use to send emails (whether you send it via Gmail or you send it via Mailchimp/GetResponse or by your own email server) or just words in your email. It is a combination of all the above factors, and there are no factors that completely determine whether your email go into the inbox or not. What you should do is follow the tips given above on how to ensure your email follow the standards, increase the ability of email to be transferred and get to the inbox of the users.

In addition, I previously had a video/article on basic knowledge of email marketing, you can see more.


Bonus: Do you know the main reasons unsubscribe users and unwanted emails are? (3)

1. I get too many emails in general (26%)
2. The Emails are not relevant to me (21%)
3. I received too many emails from this company specifically (19%)
4. The emails are always trying to sell me something (19%).
5. The content of the emails is always boring, repetitive and not interesting to me (17%).
6. I don’t have time to read the emails (16%)
7. I received the same ads and promotions in the email that I get in the print form (13%).
8. The Emails are too focus on the company’s needs, and not enough on my needs (11%)
9. The emails look cluttered and sloppy (10%).
10. I do not trust the emails to provide me the information I need to make purchase decisions (10%).
11. I get emails that do not look good on the phone (7%).

So, to have the successful email marketing tactics, each campaign needs to be cared for so that each customer gets the suitable segmentation & customization, with the appropriate frequency. It is not about sales, but more about delivering the exciting content based on what the customer wants, with a professional design and, especially, mobile compatibility.

Hope this article will help you better understand why your email can go into inbox or why not and what you can do to improve it. If you have any suggestions or opinions to add, leave a comment below!