Why am I seeing a sudden increase in Gmail 'mailbox full' deferrals?
Summary
What email marketers say10Marketer opinions
Email marketer from Email Geeks suggests suppressing unengaged contacts to address full mailboxes.
Email marketer from Litmus discusses bounce management, saying a sudden increase in 'mailbox full' bounces could indicate a stale list that needs cleaning, as recipients may have stopped actively using their old accounts.
Email marketer from StackOverflow mentions that an uptick in 'mailbox full' errors might be due to increased spam filtering, causing users to abandon old accounts without deleting messages.
Email marketer from MailerQ Blog explains that deferrals with 'mailbox full' errors can indicate the recipient's mailbox is indeed full, or, less commonly, temporary server issues on the recipient's side. It is worth re-attempting delivery before removing.
Email marketer from Email Geeks confirms that they've observed the same issue, particularly during the same period this year.
Email marketer from Mailjet shares that 'mailbox full' bounces are often temporary, but persistent occurrences mean the recipient is unlikely to clear space. Consider suppressing after repeated bounces.
Email marketer from SparkPost Blog explains that mailbox full bounces occur when the recipient's mailbox has exceeded its storage limit. This is a soft bounce and retries may be attempted.
Email marketer from Reddit suggests immediately suppressing recipients who trigger mailbox full errors to avoid further delivery attempts and protect sender reputation.
Email marketer from Email Geeks explains that Mailbox Full bounces aren't related to new requirements but depend on the target audience and engagement level.
Email marketer from EmailOctopus Blog shares that a sudden increase in bounces, including mailbox full errors, could be due to changes in recipient behavior, list quality issues, or deliverability problems requiring list cleaning and authentication checks.
What the experts say2Expert opinions
Expert from Spam Resource, Steve Jones, discusses bounce management strategies, noting that a spike in 'mailbox full' bounces often suggests that your list needs immediate attention and cleaning because these addresses aren't actively maintained, or the mailbox is full. He recommends having suppression rules to ensure these email addresses don't receive more email from you.
Expert from Word to the Wise, Laura Atkins, responds to a question about dealing with email engagement issues, she mentions that a sudden increase in mailbox full bounces could be an indicator of list decay. She recommends using list hygiene practices, such as removing unengaged subscribers.
What the documentation says3Technical articles
Documentation from Google Support explains that a 452 error related to insufficient mailbox space means the user has exceeded their storage quota. Direct users to the support article on managing storage.
Documentation from RFC 5321 (SMTP standard) describes that 4xx error codes indicate transient failures, like a full mailbox. The sending system should retry delivery later.
Documentation from AWS Documentation notes that 'mailbox full' bounces often stem from recipients not regularly checking their email or having exceeded storage limits. Implementing a feedback loop and suppressing hard bounces improves deliverability.