Published: 3 July, 2021

Prevent emails to Gmail and Yahoo and other free ISPs from being blocked or sent to spam

Gmail and other free email providers can be a challenge to get emails delivered to. We have done a fair amount of research to ensure that your emails get delivered to the various Gmail accounts in your database and mailing lists. This can also apply to other free email providers like (Microsoft) and (Apple). Using the tips in the article will reduce the likelihood that Gmail blocks your messages or marks your messages as spam. Large email providers such as Gmail, AOL and Yahoo generally follow these guidelines.

Account notification messages:

  • Check regularly to make sure that your domain isn’t listed as unsafe with ProFundCom’s delivery studio. To check your domain status, enter your domain on the Google Safe Browsing site status page. Also, check any domain that’s linked to yours.
  • Don’t send sample test campaigns from your domain. Your domain’s reputation might be negatively affected, and your domain could be added to Internet blocklists.
  • Don’t impersonate another domain or sender without permission. This practice is called spoofing, and it can cause your email to categorise the messages as spam.
  • Messages that have a From address in the recipient’s Contacts list are less likely to be marked as spam.
  • Occasionally, valid messages may be marked as spam. Recipients can mark valid messages as not spam, so future messages from the sender should be delivered to the inbox.
  • Make sure your messages are authenticated

Authenticated messages

Authenticated messages are less likely to be marked as spam. This helps protect recipients from malicious emails, such as phishing messages. These messages are less likely to be rejected or marked as spam. If you use a domain hosting service or an email provider, use the provider’s instructions for setting up authentication. Set up authentication for each of your sending domains.

To minimise the chance of your messages being marked as spam, set up these authentication methods:

  • Publish an SPF record for your domain. SPF prevents spammers from sending unauthorised messages that appear to be from your domain.
  • Turn on DKIM signing for your messages. Receiving servers use DKIM to verify that the domain owner actually sent the message.
  • Publish a DMARC record for your domain. DMARC helps senders protect their domain against email spoofing.
  • For SPF and DKIM to authenticate a message, the message From: header must match the sending domain. Messages must pass either the SPF or the DKIM check to be authenticated.

Send emails to engaged users

  • Send emails only to users who choose to receive and read your messages. They’re less likely to report messages from your domain as spam.
  • If messages from your domain are often reported as spam, future messages are more likely to be delivered to the spam folder. Over time, many spam reports can lower your domain’s reputation.
  • Get detailed information about your IP and domain’s reputation with ProFundCom’s Delivery Studio.
  • Make sure that users subscribe
  • Use these methods to help ensure you’re sending to engaged users:
  • Make sure that users opt-in to receive emails from you.
  • Confirm each recipient’s email address before subscribing them.
  • Consider periodically sending messages to confirm users want to stay subscribed.
  • Consider unsubscribing users who don’t read your messages.
  • Let users unsubscribe

Always give users a way to unsubscribe from your messages, and make unsubscribing easy. Letting users opt-out of your messages can improve message open rates, click-through rates and sending efficiency.

These are some recommended unsubscribe methods:

  • Include a prominent link in the message that takes users to a page for unsubscribing.
  • Let users review the individual mailing lists they’re subscribed to. Let them unsubscribe from lists individually, or all lists at once.
  • Automatically unsubscribe users who have multiple bounced messages.
  • Periodically send a confirmation message to users to make sure they still want to receive your messages.
  • Use one-click unsubscribe
  • To let users unsubscribe, set up one-click unsubscribe. Include one or both of these headers in your messages: List-Unsubscribe-Post: List-Unsubscribe=One-Click

Avoid these practices

  • Don’t purchase email addresses from other companies.
  • Don’t send emails to users who didn’t sign up to receive messages from you. These recipients might mark unwanted messages as spam. Future messages from your server to these users are marked as spam.
  • Avoid opt-in forms that are ticked by default and that automatically subscribe users. Some countries/regions have restrictions for automatic opt-in. Check the laws in your country/region before opting in users automatically.
  • Monitor senders who use your email service

When senders use your email service to send emails, you’re responsible for the sender’s email activity. You should:

  • Provide an email address for message recipients to report email abuse, for example:
  • Maintain updated contact information in your WHOIS record and on
  • Immediately remove any user or client who sends spam with your service.
  • Monitor affiliate marketers
  • Affiliate marketing programmes offer rewards to companies or individuals that send visitors to your website. However, spammers can take advantage of these programmes.

If your brand is associated with marketing spam, other emails sent by you might be marked as spam. You should monitor affiliates, and remove any affiliates that send spam.

Format messages according to the Internet Format Standard (RFC 5322).

If your messages are in HTML, format them according to HTML standards.

Don’t use HTML and CSS to hide content in your messages. Hiding content might cause messages to be marked as spam.

  • Message From: headers should include only one email address, as shown in this example:
  • From:
  • Include a valid Message-ID header field in every message (RFC 5322).
  • Links in the body messages should be visible and easy to understand. Users should know where they’ll go when they click links.
  • Sender information should be clear and visible.
  • Message subjects should be relevant and not misleading.
  • Authenticating domain
  • Envelope from domain
  • Payload domain
  • Reply-to domain
  • Sender domain
  • Increase sending volume slowly

If you send a lot of messages, we recommend that you:

  • Send emails at a consistent rate. Avoid sending emails in bursts.
  • Start with a low sending volume, then slowly increase the volume over time.
  • As you increase the sending volume, regularly monitor the sending rate and any responses you get. Regular monitoring lets you turn down the sending volume when the sending rate is limited, or when you start seeing errors.
  • As you gradually increase your sending volume, use ProFundCom’s Delivery Studio to monitor email performance

These factors affect how quickly you can increase sending volume:

  • The amount of emails sent: The more emails you send, the more slowly you should increase sending volume.
  • The frequency of sent emails: You can increase the sending volume more quickly when you send daily instead of weekly.
  • Recipient feedback about your messages: Make sure that you send only to users who subscribe to your emails, and give users an option to unsubscribe.

Monitor your sending volume

Important: For work and school accounts, sending limits apply even when recipients are in different G Suite domains. For example, you might send emails to users with email addresses that have the domains and Although the domains are different, if both domains have as their MX record, messages sent to these domains count towards your limit.

Monitor shared IP address reputation

A shared IP address (shared IP) is an IP address used by more than one email sender. The activity of all senders on the shared IP impact the reputation of everyone using the IP.

Use ProFundCom Delivery Studio to monitor sent emails

  • When users mark your messages as spam
  • Why your messages might not be delivered
  • Your domain or IP reputation and its impact on message delivery rates

Fix the source of rejected emails

If your messages are rejected, you might get an error message. Learn more about the error so you can fix the problem. Common error messages are:

  • 421, “4.7.0”: Messages are rejected because the sending server’s IP address is not on the allowed list for the recipient’s domain.
  • 550, “5.7.1”: Messages are rejected because the sending server’s IP address is on an IP suspended list. You might get this error if you’re sending emails using a shared IP with a poor reputation.

SMTP error reference

  • Fix bounced or rejected emails
  • Fix IPv6 authorisation errors
  • An IPv6 authorisation error could mean that the PTR record for the sending server isn’t using IPv6. If you use an email service provider, confirm they’re using an IPv6 PTR record. Here’s an example of an IPv6 authorisation error: 550-5.7.1: Message does not meet IPv6 sending guidelines regarding PTR records and authentication.


Original Source: Troubleshooting for senders with email delivery issues

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