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High bounce rates

Your bounce rate is the percentage of email addresses that your campaign could not be delivered to. Email providers and anti-spam networks monitor bounce rates for every campaign you send, and use that information to decide if they'll accept mail from you in the future.

Besides affecting an individual sender's reputation, high bounce rates can land our sending IPs on blacklists, and potentially affect others who use our service.

While we do a lot of work behind the scenes to protect you from potential problems, there are certain best practices you can follow to keep things running as smoothly as possible.

As a guideline, a well maintained, permission-based list should typically see bounce rates of 2% or less for each email campaign sent.

What causes high bounce rates

Bounce rates are often related to the quality of your contact audience. Low bounce rates are a good indication of a healthy, permission-based list with active and engaged subscribers. High bounce rates indicate there may be problems with the way your audience has grown, or how it is being managed.

Here's an example:

An email marketer sends a campaign to a group of 3,000 subscribers that they have not emailed in 12 months. Because the list is stale, many of the email addresses are no longer in use and 300 Yahoo addresses bounce the email for this reason. Another 150 Yahoo addresses on the list get the email, this time.

Next time the email marketer sends a campaign, Yahoo's servers immediately identify that there was previously an issue, and it was for a pretty big number of their customers' mailboxes. As far as the email provider is concerned, this marks the sender as a spammer, and since they want to protect their customers, all incoming mail is blocked this time. Even the 150 contacts who got the last campaign — including those who opened or clicked a link in it — are not delivered to.

Whether the ISP blocks the campaign outright or sends it to its junk folder, the email marketer's reputation is damaged. News spreads quickly to blacklist operators and anti-spam networks, which all of the major ISPs subscribe to. If nothing is done by the marketer to rectify the situation, email deliverability to other major ISPs will soon decline.

How to prevent bounces

There are a number of things you can do to keep your bounce rates low.

Don't send to stale contacts

As explained in the example above, sending to stale contacts — that is, contacts that have not had a campaign sent to them for six months or more — is not a good idea.

Most people don't keep the same email address for life — people change jobs or retire, change names, switch Internet or email providers, or let their domains expire. Some free email providers even close accounts after a certain period of inactivity.

Given enough time, most email addresses will stop working and start returning bounces. Really old email addresses that have been dormant for 18 months or more are also at risk of becoming recycled as spam traps.

If you haven't sent an email to your subscriber list in six months or more, you may want to send a subscription reconfirmation email to keep things fresh. This can also be a good idea for users who have been inactive for six months or more.

Never use purchased lists

Our Anti-Spam Policy doesn’t allow the use of purchased, rented or third party lists. There's no way to verify how old the addresses on a bought or borrowed list are, nor do you know if permission was obtained from the people on the list.

Many list vendors build their databases by harvesting email addresses from thousands of websites, which means you could easily end up sending to a pure spam trap.

Remove invalid email addresses

When new subscribers join your audience through a signup form, either online or offline, they may make an error or deliberately enter fake details.

While you can check each of your contacts manually for incorrectly formatted addresses, invalid domains, and typos, most issues can be solved by asking your newly added contacts to confirm opt-in.

Never use free webmail addresses

You have a higher chance of your campaign reaching the inbox if you don't use a free webmail account as your "From" address, as this is something mailbox providers actively look for when trying to determine if a message is spam.

Learn more about the importance of "From" names and addresses

Avoid spammy content

While some ISPs will direct email to the junk folder if it reads like spam, others will block it outright. Try to avoid spammy language in your campaigns.

Suppress previous bounces

If you're making the move from another ESP, and you have access to your previous bounce reports, make sure to keep these addresses separate from your active list when transitioning over to us. As an extra precaution, you should move the bounced addresses to error status so that they are not re-engaged.

What we do to prevent bounces

Bounces are a reality of email, and although the reasons for a bounce can be outside of our control, we do a lot behind the scenes to maintain deliverability and sender reputation.

Our target is 98% acceptance rates of valid mail sent from our network, and we consistently achieve that level. We do this through constant monitoring of our outgoing IP addresses, as well as direct contact with email providers including Gmail, Yahoo, AOL, Hotmail, and a significant number of local providers on a global basis. We limit mail delivery attempts to a period of 30 hours so you can be made aware of, and respond to, any issues in a timely fashion.

We're constantly monitoring our network for blacklistings and technical changes that may interfere with the delivery of messages. If there's a problem, we suspend the identified part of our network while we work with blacklist maintainers and affected ISPs to rectify the issue.

Additionally, if an account shows abnormally high bounce rates we will follow up with the account holder in order to resolve the situation.

What to do if high bounce rates persist

If you've followed our prevention guidelines and you're still seeing high bounce rates, there's a few things you can do to further improve your deliverability.

You may want to consider using list segmentation to send to your most engaged customers first, followed by those who are less engaged. This will "train" the email provider's spam filter in regards to your content, showing higher levels of engagement from the start and setting you up for positive results with future campaigns.

If you see a sudden surge in bounces compared to your usual level, you may also want to take a look at your response data to look for a common theme. There could be a single domain that has blocked a large portion of your emails.

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