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Factors Affecting the Delivery Rate of Outgoing Emails

[As of September 2023]


100% email delivery cannot be guaranteed for various reasons.

Here are the main factors that can affect delivery:

Technical Factors

  1. Server Outage: If the target mail server or the SMTP relay itself fails, the email will not be delivered.
  2. Network Issues: Connection problems between servers can lead to delays or delivery failures.
  3. Spam Filters: Aggressive spam filters can block legitimate emails.
  4. Misconfigurations: Errors in DNS entries, SPF, DKIM, or DMARC can affect delivery.
  5. Size Limitations: Some mail servers have restrictions on the size of emails they can accept.
  6. Rate Limiting: Many mail servers limit the number of emails that can be sent from a single IP address within a certain period.

Human Factors

  1. Incorrect Email Address: A typo in the recipient's email address can result in the email not being delivered.
  2. Recipient Action: The recipient can mark the email as spam or set up rules that automatically delete the email.
  3. Access Issues: The recipient may have trouble accessing their email account, e.g., due to a forgotten password or locked account access.

Legal and Compliance Factors

  1. Data Protection: In some cases, legal regulations can prohibit or restrict the delivery of emails.
  2. Blacklisting: The IP address or domain name of the sending server could be on a blacklist.
  3. Content Review: Some countries or organizations have strict rules for the content of emails that can affect delivery.

Other Factors

  1. Time Limitation: Sometimes emails are held in the queue for a limited time and then deleted if they cannot be delivered.
  2. Manual Review: In rare cases, manual review may be required, delaying delivery.

Due to these many variable factors, it is not possible to provide a 100% delivery guarantee for emails.


LSP.net measures to increase the delivery rate: SMTP Relay Service with high reputation and GDPR compliance.


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