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Gmail deliverability best practices

Gmail has high standards for marketers sending to their servers and expect them to consistently follow sending best practices. You can receive additional insight into Gmail by reviewing Return Path’s Marketers Field Guide to Gmail, Yahoo and Outlook. This guide gives great information about Gmail and how they determine what email is filtered to the spam folder and what email reaches the inbox.

It is important to note that deliverability problems at Gmail aren’t solved over night and may be caused by a variety of issues related to your subscriber acquisition and data hygiene process, as well as other factors related to your infrastructure or the effectiveness of your content keeping subscribers engaged.

Gmail recommends:

  • Follow their bulk sender guidelines to improve inbox placement rates.
  • Sign up with their postmaster tools to help you analyze your performance and become a better sender. It is a crucial step in identifying trends to determine if one factor is heavily influencing the spam folder placement you are experiencing.
  • When using the postmaster tools and you see issues or negative dips in performance, Gmail expects you to take action as soon as possible to identify and fix the root cause. 

Gmail’s top deliverability factors:

  • Complaints: A high complaint rate can cause your email to be filtered to the spam folder. It tells Gmail that you are sending to Gmail users who don’t want your email and may signal that you are more likely a spammer. Gmail likes when subscribers rescue your email from the spam folder if it is marked as spam. It tells Gmail that you are more likely a legitimate sender.
  • Engagement: Send relevant email to your subscribers so they interact with it regularly. When encountering deliverability issues at Gmail, temporarily sending only to your most engaged subscribers (those who have engaged within the last 15 or 30 days) can help improve your sending reputation and lead to an increase in inbox placement. Gmail uses engagement as a factor for filtering your email.
    • Gmail looks at how engaged each subscriber is with your domain relative to other domains and factors that into filtering decisions. This type of relative engagement may be adjusted based on your sending reputation.
  • Authentication: Ensure you are authenticating with Sender Policy Framework (SPF), Domainkeys Identified Mail (DKIM) and Domain-based Message Authentication Reporting & Conformance (DMARC). Ensure that there are no configuration errors in all of the authentication methods or it could lead to messages sent to the spam folder.
  • New IP address or domain: Warm up all new IP addresses and new domains to establish a sending reputation. Neglecting to warm up your new IP address or domain causes email to be sent to the spam folder. If you are having difficulty reaching the inbox at Gmail using "normal" warm up volumes, follow these general guidelines:
    • Start with a very low volume of messages every few hours for the first few days. Do not exceed 500 messages in one day. 
    • Send only to highly engaged subscribers in the beginning.
    • Monitor performance using your bounce logs and Inbox Monitor to see how Gmail reacts.
    • Once your messages are reaching the inbox, double volumes every 3-4 days. Keep monitoring performance.
    • If you encounter spam folder placement, slow down or pause the volume for several days to allow Gmail's spam filter to adjust.

Gmail's deliverability best practices:

Infrastructure

  • Ensure your IP address (IPv4 or IPv6) has a valid, non-generic rDNS (PTR) record. IPv4 is the most common format for sending IP addresses at this time. Sending IP addresses without an rDNS record will be marked as spam or rejected.
  • Use Forward Confirmed Reverse DNS (FCrDNS) for sending IP addresses and their corresponding hostnames.

Use a dedicated IP address

  • Using a dedicated IP address makes it easier for Gmail to identify you. Gmail also uses domain-level reputation in filtering decisions, but a dedicated IP address makes the delivery path from your ESP easier to determine and track.
  • A dedicated IP address may not be practical or possible for some smaller volume senders. Talk to your email administrator or ESP about your options. If you have to send from a shared IP address, follow Gmail's guidelines as listed in this article as closely as possible.

Authenticate your email

  • Authenticate your email using Sender Policy Framework (SPF), Domainkeys Identified Mail (DKIM) and Domain-based Message Authentication Reporting and Conformance (DMARC).
    • Full domain alignment (using the same domain) of the MFrom, Sending From and DKIM d= domain makes it easier for Gmail to identify you.
    • Work towards a DMARC p=reject policy over time. Be sure to monitor DMARC reports with a p=none policy first or you put yourself at risk of getting your legitimate email blocked should the DMARC record be set up incorrectly.
    • Authenticated email tells Gmail that you are less likely a spammer.
  • Authenticating your email is especially important if you send email from an IPv6 IP address. Your sending domain should pass SPF and DKIM checks or your email may be marked as spam.

Sender permanence

  • Consistently send from the same sending infrastructure and IP addresses. Be mindful of using IP addresses that are only used for special events, such as a conference. Gmail can identify sending patterns for domains and IP addresses, so suddenly sending from IPs and domains that typically only send email a few times per year can result in spam folder placement.

Security

  • Use Transport Layer Security (TLS). TLS is a protocol that ensures that the communication between two servers or applications is secure and that no third party is able to tamper with the message.
  • Use Hypertext Transfer Protocol Secure (https) for your web page links. Using https helps protect data from being snooped by third parties, such as in public wifi hotspots.

Keep your HTML code clean and concise

  • Messages over 102 KB will be clipped by Gmail when being viewed by a subscriber. This could impact how subscribers interact with your email.
  • Use Inbox Preview to help identify possible HTML issues.

Send to engaged subscribers

  • Be more aggressive with your list hygiene program to remove unresponsive Gmail subscribers from your email list. This is especially important if your email is consistently being placed in the spam folder. Over time, continually sending email to subscribers when your email is landing in the spam folder will cause more email to be sent to the spam folder.
    • In the absence of a Gmail complaint feedback loop where they send you complaint messages (like many traditional feedback loops), your list hygiene policy and process is very important.
  • Sending to engaged subscribers reduces your complaint rate, increases the number of people rescuing your email from the spam folder (this is not spam) and increases your response rate.
  • Allow and encourage subscribers to reply to your email. Engaged subscribers typically don't reply to email sent from a spammer, so it helps Gmail see that you are more likely a legitimate sender.
  • Send to engaged subscribers early and the unengaged subscribers later in the day. If you send to unengaged subscribers early in the day, the poor sending metrics can affect the deliverability of your campaigns for the rest of the day.

Have a solid opt-in process

  • Use opt-in permission methods. Don’t assume a subscriber or customer wants to receive your email.
  • You should verify each email address before adding them to your list.
  • Do not assume customers who purchased a product or signed up for a website are interested in receiving email; ask them specifically to opt-in.
  • Set clear expectations up-front about email content and frequency.
  • Do not auto-check the opt-in box on a web form.

Identify campaigns leading to high complaint rates using Gmail’s complaint feedback loop

Classify your email

  • Send different categories of mail (for example, promotions, transaction notifications, social updates) from different sender addresses and keep those addresses consistent over time.
  • Avoid mixing different categories of content in one email. For example, you may want avoid putting a promotional message into a transactional mail notification because it may make the system classify the message as promotional.

Pay attention to and customize sending frequency

High frequency senders generally see more spam folder placement at Gmail.

  • Allow subscribers to select the frequency at which they receive messages at opt-in through the use of a preference center.
  • Mail less frequently to subscribers who are less engaged. Do not send a daily email to a subscriber who is not opening them.

Segment mail streams

  • Use different sub-domains, domains, and IP addresses for different mail streams (for example, marketing versus transactional messages). Segmenting gives greater control to the subscriber, allowing them to unsubscribe from one stream, while staying subscribed to others.
  • Segmenting also makes it easier for you to troubleshoot issues should they occur.

Unsubscribe process

  • Make the unsubscribe process easy and straight forward. Use a one-click process and do not require a user to login to their account in order to unsubscribe.
  • Immediately add users that unsubscribe to a suppression list. The longer you wait and the more email you send to a user after they unsubscribe contributes to a negative sending reputation at Gmail.
  • Include an unsubscribe link in every email and honor all unsubscribe requests.
  • Allow subscribers to unsubscribe from specific email streams.
  • Allow subscribers to unsubscribe from all email streams using a global unsubscribe option.
  • Include a List-Unsubscribe header. Gmail supports both the mailto: and URL options. This is not a substitute method for unsubscribing.
  • Unsubscribe unknown users after one bounce.

SMTP error codes

  • Track and monitor bounce message error codes from Gmail in order to help identify and fix issues. They can be an important indicator to Gmail about the health of your email program.
  • Gmail SMTP error codes.

Use responsive design

  • 75% of Gmail users access their accounts on a mobile device. (Techcrunch)
  • As of August 31, 2016, Gmail now supports responsive design media queries for bulk email senders.
  • Responsive design helps your email render better in mobile devices, leading to a better customer experience, and possibly an increase in response rates.
  • Validate CSS prior to deployment to ensure there are no errors.

Don’t send malicious URLs in your content

  • Ensure that your sending domains and the domains in your content are not hosting malware or are known phishing websites. Although Gmail doesn’t publicly disclose how they identify dangerous websites, you can check:

Take responsibility for all email sent from your system or on your behalf

  • You are responsible for all email sent from your system by a third party, whether or not the email is authorized. Be sure that a third-party using your system is well vetted and you are keeping track of their sending practices and performance. Disallow any third-party from using your system if they send spam.
  • Closely monitor the sending behavior of companies you use for affiliate marketing. Many affiliate marketing vendors do not follow sending best practices which can harm your brand and domain reputation, and cause your email to go to the spam folder.
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