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Most common Gmail spam problems and how to address them
Written by
Dibya Sahoo
dibya.sahoo
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Most common Gmail spam problems and how to address them

Gmail never talks about its spam detection logic. There are a few official resources that explain why a specific type of email gets classified as spam. However, there is still no detailed explanation on each of the spam notifications. This tutorial aims to consolidate facts, observations, and expert opinions to help you understand the exact reason for some of the Gmail spam notifications.


Gmail never talks about its spam detection logic. There are a few official resources that explain why a specific type of email gets classified as spam. However, there is still no detailed explanation on each of the spam notifications. This tutorial aims to consolidate facts, observations, and expert opinions to help you understand the exact reason for some of the Gmail spam notifications.


Disclaimer: There is no one solution for all types of Gmail spam problems. Please feel free to comment below with your specific deliverability challenge, and I will try to address that or include the solution as a part of this tutorial. 

#Error1: This message seems dangerous. Similar messages were used to steal people’s personal information. Avoid clicking links, downloading attachments, or replying with personal information.

Criticality: HIGH

Gmail Warning Message:



Solution: For Gmail Users


If you have received an email with a spam notification at the top, avoid doing any email engagement.

  • Don’t click any link inside the email
  • Don’t download any attachments
  • Don’t reply to these emails.

Gmail’s anti-spam engine marks suspicious emails as spam and discourages everyone from taking any action on such emails. These emails may be containing some suspicious links or attachments which may steal personal information.

However, there can be cases where Gmail might have incorrectly classified a good email as suspicious. In such a case, you can report Gmail by clicking on “Not spam” or “Looks safe” button.

Solution: For Email Senders

If you are the sender of an email message flagged with “This message seems dangerous” spam notification, try checking the potential problems with links, sender domain, and attachments. It is hard to find the exact problem, but you can use tools to debug a few potential issues.


1. Potential problems with links

The warning message says avoid clicking links, this is a clear indicator of having potential issues with your link URLs. You should check and ensure that all of the URLs are following the below email best practices:


(a) No broken URL should be there: Test your emails thoroughly before sending. Any broken links within your email may create insecurity with your users and increase the abuse complaints. Typo mistakes within the links can get users redirected to parked webpages which can potentially steal personal information.


(b) URL domain should not be on blocklist: There are 100+ global blocklist databases referred to as DNSBLs and RBLs. Most leading Network and Service providers refer to these blocklists to filter our spam from their network. There is no public documentation on which blocklist databases probably Gmail might be using. However, trends indicate that domains which are part of any critical blocklists like SpamCop, Spamhaus, barracuda, or others will be having a higher chance of their emails getting flagged as spam. You can use tools to check the blocklist status of your URL domain.


(c) Please don’t use any free or public URL shortener: Spammers widely use public URL shorteners to hide their long phishing URLs behind the curtain. Because of this reason, most URL shorteners like Bitly, goo and others carry bad email reputation. Email best practices recommend not using any URL shortener domain within your emails.


(d) Landing URLs should not be directly asking for personal information: You must check that your information capturing forms are well-protected behind a login and are not open-ended. Open-ended forms asking for critical personal information like Credit Card, Phone number and so on are vulnerable to being flagged as suspicious by the anti-spam engine. Open pages asking for such information will have higher chances of getting flagged as suspicious.


(e) Avoid the use of spam triggering phrases in the URL: You should avoid the using words like “earn extra income”, “you won”, “lottery” and so on. This phrases historically carries a very bad email reputation. You are free to use these words only if you have a genuine business use case with your optin subscribers. Gmail’s anti-spam engine is much smarter today to ignore such valid business cases.


(f) Domain WHOIS is not associated with any known spammer networks: Make sure you do not have a default WHOIS record for any of your URL domains. Instead, WHOIS can either be privacy protected or should be carrying valid information about your company. Sometimes the default entry might be associated with a known spammer network.


(g) Avoid using Non-HTTPS links: Google has started putting a strict check on the non-HTTPS traffic on its Chrome browser. Most security policies are standard among Google’s product line, and this is why Gmail is also bound to have some strict measures around this HTTPS policy. Email best practices recommend the use of HTTPS links within the email. If you have redirections on your URL, then make sure the source to destination, all the URLs are on HTTPS. Example: You might be having a URL track.example.com in your email, which on click getting redirected to test.com and finally to abc.com. You should make sure all the URLs in this journey are using valid HTTPS; https://track.example.com –> https://redirect.test.com –> https://destination.abc.com. Since URLs are the main gateway for clicks, it makes complete sense to follow all email best practices to ensure your links look trustworthy and not getting flagged suspicious.


2. Potential problems with attachments

Use attachments only if it’s required. In marketing emails, you should avoid using any attachments. Sending bulk attachments is a common reason for triggering any spam filters. Having said that if there is a valid business case to send attachments, then use it but follow the below best practices:


(a) Size of the attachment should be below 80Kb: Best practice recommends to keep the email size below 100KB. This means your attachment size should not be more than 80Kb, because you will always have to keep some buffer for the HTML content and email headers too.


(b) Pre-scan attachments for any potential viruses: Make sure you have used the right set of tools to pre-scan your attachments for any possible virus.


(cType of attachments: PDFs are the most acceptable form of attachments to include. Sending anything else with your bulk emails like a .zip, .docx or an executable file will be having a higher chance of getting trapped in the spam filter’s radar. List of attachment files or extension types blocked by Gmail: .ade, .adp, .apk, .appx, .appxbundle, .bat, .cab, .chm, .cmd, .com, .cpl, .dll, .dmg, .ex, .ex_, .exe, .hta, .ins, .isp, .iso, .jar, .js, .jse, .lib, .lnk, .mde, .msc, .msi, .msix, .msixbundle, .msp, .mst, .nsh, .pif, .ps1, .scr, .sct, .shb, .sys, .vb, .vbe, .vbs, .vxd, .wsc, .wsf, .wsh. In case you are sending a compressed zip file, make sure it doesn’t contain any of the above file extensions. You can send up to 25 MB in attachments. If you have more than one attachment, they can’t add up to more than 25 MB. If your file is greater than 25 MB, Gmail automatically adds a Google Drive link in the email instead.

(d) Avoid one-click download URLs.


3. Potential problems with the sender domain or sender email address


The SPF and DKIM signing domains’ reputation is important in achieving a high deliverability rate with Gmail. If your emails are getting into the spam folder, you must check your sender domain’s reputation on Google Postmaster. Gmail categorizes each domain’s reputation into four categories:


(a) Bad: Gmail assigns a BAD reputation score to domains with a history of sending an enormously high volume of spam. Most of the emails coming from these domains will get rejected at Gmail’s SMTP level. However, few emails still might escape this check but will mostly get delivered with a “Spam Warning Message” on the top.


(b) Low: Gmail assigns a LOW reputation score to domains with a history of sending a considerable volume of spam. In the case of LOW reputation, emails are accepted at SMTP but mostly classified as spam. 


(c) Medium/Fair: Gmail assigns a Medium/Fair reputation score to domains which usually send good emails, but might have occasionally sent a small volume of spam. In case of Medium reputation, you will get a decent email deliverability rate with lesser number of emails landing in spam.


(d) High: Gmail assigns a High reputation score to domains who complied with Gmail’s sender policies and has an excellent track record of sending very good emails with almost zero spam. Sender domains with high postmaster reputation will rarely get classified into spam.

#Error2:  Why is this message in spam? It is similar to messages that were identified as spam in the past.


Criticality: HIGH

Gmail Warning Message:


Solution: For Gmail Users


Suppose you have received an email with a spam notification saying “It is similar to messages that were identified as spam in the past”. Then this means that other users reported similar messages as spam. These emails are mostly not a phishing or spoofing attempt. Instead, these are the emails which probably sent on a non-optin user list. Generally, in such a scenario, people mark the emails as spam. Before replying or engaging on these emails, you should first verify the sender and see if the brand is known to you.

If Gmail has mistakenly classified an email from one of your trusted source as spam, then you can choose to move such emails to either inbox or report to Google by clicking on “Not Spam”.

Solution: For Email Senders


“It is similar to messages that were identified as spam in the past” – If you are getting this spam notification in your emails, then try checking the potential problems with links, sender domain and more importantly the source of the target list. It is hard to find the exact problem, but you can use tools to debug the potential issues and see if fixing them helps get your emails unflagged from spam.

1. Potential problems with links

Despite being a good sender, if you mistakenly include a link in your email which is not trusted or blocklisted then the chances of your emails landing in spam increases. Here is a live example where Google’s email itself got classified as spam because of one potential bad link in the email. For privacy purpose, the URL in the email is masked to example.com.

2. Potential problems with the sender domain or sender email address


The SPF and DKIM signing domains’ reputation is important in achieving a high deliverability rate with Gmail. If your emails are getting into the spam folder, you must check your sender domain’s reputation on Google Postmaster. Gmail categorizes each domain’s reputation into four categories:

(a) Bad: Gmail assigns a BAD reputation score to domains with a history of sending an enormously high volume of spam. Most of the emails coming from these domains will get rejected at Gmail’s SMTP level. However, few emails still might escape this check but will mostly get delivered with a “Spam Warning Message” on the top.

(b) Low: Gmail assigns a LOW reputation score to domains with a history of sending a considerable volume of spam. In the case of LOW reputation, emails are accepted at SMTP but mostly classified as spam. 

(c) Medium/Fair: Gmail assigns a Medium/Fair reputation score to domains which usually send good emails, but might have occasionally sent a small volume of spam. In case of Medium reputation, you will get a decent email deliverability rate with lesser number of emails landing in spam.

(d) High: Gmail assigns a High reputation score to domains who complied with Gmail’s sender policies and has an excellent track record of sending very good emails with almost zero spam. Sender domains with high postmaster reputation will rarely get classified into spam.

Here are few other Gmail Spam Notifications


#Error 3: Why is this message in spam? Lots of messages from example.com were identified as spam in the past.


#Error 4: Be careful with this message Gmail could not verify that it actually came from hr@example.com. Avoid clicking links, downloading attachments, or replying with personal information.


#Error 5: Gmail couldn’t verify that abc@example.com actually sent this message (and not a spammer).


Conclusion


So, these were some of the most common Gmail notifications that you might have received which are important to understand and take actions upon. Hope, this blog is able to help you find a perfect solution to some of your Gmail Spam issues.

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