When emails don't get through

Sender Policy Framework (SPF)

What is SPF?

Sender Policy Framework (SPF) is an email authentication standard that helps protect email senders and recipients against spoofing and phishing attacks. By defining which IP addresses are authorized to send emails for a specific domain, SPF enables receiving mail servers to verify if an incoming email has originated from an approved source.

Why is SPF important?

SPF is crucial in preventing spammers from using a domain to send fraudulent emails. It can also increase the chances of emails being delivered to the recipient's inbox, rather than being marked as spam or being blocked altogether.

How can SPF issues affect email delivery?

• An improperly configured SPF record can cause emails to be rejected, quarantined, or marked as spam. Common SPF-related issues include:
• Missing SPF record:
  The sender's domain lacks an SPF record, making it difficult for receiving mail servers to verify the email's legitimacy.
• Misconfigured SPF record:
  The SPF record contains errors or syntax issues that prevent correct evaluation.
• Overly restrictive SPF policy:
  A strict SPF policy may cause legitimate emails to be flagged as suspicious if they're sent from IP addresses not listed in the SPF record.

DomainKeys Identified Mail (DKIM)

What is DKIM?

DomainKeys Identified Mail (DKIM) is an email authentication method that uses cryptographic signatures to verify if an email has been tampered with during transit. It allows the receiving mail server to check that the email was actually sent by the claimed sender and ensures the message's integrity.

Why is DKIM important?

DKIM adds an additional layer of security to the email authentication process, making it more challenging for spammers to forge or alter emails. Properly implemented DKIM can also improve email deliverability and enhance sender reputation.

How can DKIM issues affect email delivery?

DKIM-related issues that may impact email delivery include:

• Missing DKIM signature: If an email lacks a DKIM signature, it may be considered less trustworthy by receiving mail servers.
• Invalid DKIM signature: A DKIM signature might be considered invalid if the private key used to sign the email doesn't match the public key published in the domain's DNS records.
• Misconfigured DKIM records: Errors in the DKIM DNS records can prevent successful verification of the email's authenticity.

Domain-based Message Authentication, Reporting, and Conformance (DMARC)

What is DMARC?

DMARC is an email authentication protocol that combines SPF and DKIM technologies to provide greater security against email fraud. It enables domain owners to specify policies on how receiving mail servers should handle emails that fail SPF or DKIM checks, including reporting, quarantining, or rejecting them.

Why is DMARC important?

DMARC offers a comprehensive solution to protect against email spoofing and phishing attacks. By giving domain owners control over the handling of unauthenticated emails, it helps improve email deliverability and enhances sender reputation.

How can DMARC issues affect email delivery?

DMARC-related issues that may impact email delivery include:

• Missing DMARC record:
  The absence of a DMARC record can make it more challenging to detect and prevent email spoofing and phishing attacks.
• Misconfigured DMARC record:
  Errors in the DMARC record may lead to incorrect handling of emails, potentially causing legitimate emails to be rejected or marked as spam.
• Overly strict DMARC policy:
  A DMARC policy with overly restrictive settings can result in the rejection of legitimate emails that fail SPF or DKIM checks due to minor misconfigurations.

Mail server configuration and performance issues

Mail server configuration issues on the device where the emails are sent from:

This is not a web server issue, but it is still quite common. Proper configuration of the sender device is essential for successful email delivery.

SMTP (Simple Mail Transfer Protocol) settings, such as the host, port, and authentication details, need to be configured accurately to ensure emails are sent and received correctly.

Unfortunately, some devices, typically certain types of mobile phones, are not specifically user-friendly. Because of this, average users may make mistakes during setup. Typically, these settings may fail when a non-expert is about setting up a new phone or laptop.

Mail server performance issues

The performance of the sender's mail server can also impact email delivery:

• Server downtime:
  If the sender's mail server is down or experiencing technical issues, emails may not be sent or may be significantly delayed.
• High server load:
  A high volume of outgoing emails or other resource-intensive tasks can strain the mail server, resulting in slow email delivery or failures.

Blacklisting:

If the sender's mail server IP address or domain is blacklisted by anti-spam organizations, emails may be rejected or marked as spam.

Greylisting:

Read more about email delays in connection with greylisting →