Email non-delivery and complaints

Non-deliveries and complaints are a means of communicating issues for a particular recipient’s experience.

Because of this, they should be treated with the sincerity of what they represent to help protect your recipients' experience with your emails, as well as to help identify issues with your sending practices should an unexpected trend of bounces or complaints occur.

Avoiding email non-delivery and complaints is helpful for maintaining strong email deliverability, as too much of these can have a negative consequence on your sender reputation. Employing deliverability best practices will help you to do so and more easily land your email messages in your audience’s inboxes.

Email non-delivery activities

Email non-delivery can be the result of issues with the email content (an Invalid email activity) or with something on the recipient’s side (Bounced email and Deferred email activities). A complaint means that the recipient has marked your email as spam (Abuse reported). You can view email non-delivery activity under Activities and in Reports.

Invalid emails are tracked separately and are not counted within the Sent email activity. This is because the Invalid email activity occurs before an email is sent. However, bounced and deferred emails are counted within Sent email, while also being tracked as separate activities.

Bounced email (hard and soft bounces)

An email bounces when its delivery was rejected by the recipient’s mail server. The reason an email is rejected for delivery determines if that bounce is considered hard or soft.

A hard bounce means the email has been permanently rejected because the email address is invalid or doesn’t exist. For instance, a spelling error in a person’s (contact’s) email address may cause a hard bounce. Or an unused mailbox was suddenly shut down by the mailbox provider because of disuse.

A person’s email address is unsubscribed automatically after they have hard-bounced twice. We do this to ensure that your sender reputation remains high. Continuing to try to send to someone with a known bad address will harm your sender reputation, which affects how likely your email is to end up in someone’s inbox.

A soft bounce means that the email address was more than likely valid and the email reached the recipient’s mail server. However, it bounced back because of a temporary issue, like an outage on their end, or a block.

Blocks are treated as soft bounces because they are less permanent than a hard bounce. A block may be the result of your internet protocol (IP) address or domain being added to a blacklist, or a technical issue between the mail servers.

Most bounces experienced within your Ortto account are not due to an IP block, thanks to the protective sending limitations around our acceptable usage policy and the active work of our internal Deliverability team. However, if you notice a trend in bounces that you need help investigating or appear to be due to some sort of block, please reach out to our Support team by emailing

Manually resubscribe a person

You can manually resubscribe people if needed, for example to fix an email address spelling error that caused an initial hard bounce. This should generally only be done in the case where you had an incorrect email address for a contact and have corrected it.

Use caution when doing this, as continually emailing people who have previously hard-bounced will affect your sender reputation.

Learn more about editing a person’s subscription preferences under Viewing and editing a person.

Invalid email

An Invalid email activity is triggered before the email is sent. Reasons for an invalid email include:

  • the content of the email was empty

  • the person (contact) was not found or not subscribed.

Invalid email activity doesn’t have a retention limit and is tracked for the life of your Ortto account.

Deferred email

Sometimes, an attempt to deliver email results in a deferral from the recipient’s mail server. This means that the recipient’s mail server has temporarily refused delivery of an email.

If this occurs, Ortto will attempt to send the email for up to 72 hours until it is delivered (resulting in a Sent email activity). If the email still cannot be delivered over the 72-hour period, it will be considered bounced (resulting in a Bounced email activity).


Complaints are an important part of the email ecosystem, as they allow recipients to advise that the email received was perceived as spam (possibly malicious, unsolicited, undesired, and/or irrelevant).

Complaints are very harmful to a sender’s reputation, when multiple occur.

The industry-acceptable level of complaints for a permission-based sender is below 0.02% or less than 2 out of every 10,000 subscribers.

If a person marks your email as spam (Abuse reported activity), that person will automatically be unsubscribed from all email.

Should you see a string of complaints that go above the advised threshold, stop sending and check your audience subscription preferences. This experience means that subscribers believe that you are sending mail that they did not ask for, and it only takes a smaller number of these complaints to see a drop in sender reputation.