SMTP Error 552 5.2.2 – Mailbox Full: How to Fix & Prevent It

What is SMTP Error 552 5.2.2?

SMTP Error 552 5.2.2 occurs when an email cannot be delivered because the recipient’s mailbox has exceeded its storage limit. When a mailbox fills up, all new incoming emails get rejected with bounced messages with a Mailbox Full error. This problem can have devastating effects to individuals, businesses, and IT administrators—resulting in communication disintegration and delay.

This error is frequently seen in email systems with strict quota limits from the email providers such as free accounts or business accounts that have a limited storage.

Why does SMTP Error 552 5.2.2 happen?

In basic terms, SMTP Error 552 5.2.2 occurs when an email server rejects an incoming message because of a full mailbox. That being said, there are actually several factors that contribute to this issue—ranging from storage limits imposed by providers to inefficient email management practices. Below are the most common reasons why this error occurs.

ISPs or email providers set storage limits

• Most email providers, including Gmail, Outlook, and business-hosted email services, set storage quotas to manage server capacity. Free accounts often have lower limits (e.g., 15GB on Gmail), while business plans offer more storage but may still have restrictions.
• If a user exceeds their limit, new emails bounce back with the 552 5.2.2 Mailbox Full error. For instance, let’s say there’s a company using a mail server that limits individual users to 2GB each. An employee unable to clear old messages from receiving new ones will not receive new emails after some time.

Unread emails or large attachments have piled up

Emails with large attachments (like PDFs, videos, or high-resolution images) can take up a lot of storage space. Eventually, a mailbox with thousands of unread messages (especially marketing newsletters or system notifications) will reach its storage limit.

For instance, a salesperson receiving daily reports with large Excel files may unknowingly max out their quota if they don’t take the time to read and clear their inbox—causing incoming emails to bounce.

Misconfigured email settings lead to quota mismanagement

It’s also a possibility that some email accounts are set up with incorrect storage settings or retention policies. This might cause unexpected storage overflow.

For example, an email system that is set to never to delete old messages from the server (even after downloading it to a local email client, such as Outlook) can eventually cause a mailbox to reach its limit sooner than anticipated. This is often the case with IMAPs, where email does not get deleted or archived.

Automated email forwarding can create unnecessary duplicates

Email forwarding is a common feature of every mail client. However, if it is configured incorrectly, it can lead to the same set of emails piling up in multiple inboxes. If a user set up forwarding but did not check the “delete after forwarding” option, the original and forwarded emails both sit in the inbox.

For example, a business owner forwarding all their company emails to a personal Gmail account might unknowingly fill both mailboxes, eventually triggering SMTP Error 552 5.2.2.

How to fix the dreaded “Mailbox Full” error

If you’re seeing SMTP Error 552 5.2.2, it means your sender’s mailbox has reached its storage limit. The good news is that there are simple ways to fix it. Below, we’ll go through practical steps for both email users and email administrators to clear space, prevent email bounces, and ensure smooth communication.

Steps for email senders

Let’s get one thing straight. The full mailbox is the mailbox you’re trying to reach. While you can’t free up space in the recipient’s mailbox, you can still optimize your emails to improve the chances of delivery.

• Retry sending the email later: The recipient may have already cleared space in their inbox by then. You’ll have to do this manually, as this particular SMTP error does not have automatic retries or deferrals. 
• Check for alternative contact methods. If the email bounces, try LinkedIn, a phone call, or another email address.
• Monitor your bounce rate. If you repeatedly send emails to full inboxes, your sender reputation may decline. 

Steps for email recipients

You might be the sender in this case, but you should still learn the recipient side of things. You can follow these steps to guide the recipients you’re attempting to send emails to, should you be able to reach them through other means.

On the other hand, these steps can also serve as reminders for you to ensure you don’t experience the full mailbox situation. Some important emails may not find their way to your inbox if it is full.

• Check mailbox storage usage. Before fixing the issue, check how much space your mailbox is using. For Gmail/Outlook, simply go to Settings > Storage to view quota details. For business emails, do check with your IT admin or webmail settings.
• Delete unnecessary emails. Identify large emails or folders taking up space. Sort emails by size or date and delete the biggest ones first. Also remove newsletters, promotions, and old conversations. Tip: Use search filters (e.g., “larger:10MB”) to find bulky emails.
• Empty trash & spam folders. Deleted emails still take up space if they’re in the trash. Go to Trash and click Empty Trash Now. Clear the Spam folder, as it can accumulate large emails. Some email providers auto-delete trash after 30 days—don’t wait.
• Download & backup old emails using either local storage or cloud. Instead of keeping all emails in your inbox, back them up. Move important messages to Google Drive, Dropbox, or external hard drives. Consider setting up automatic email archiving in your provider’s settings.
• Increase email storage limit. If you’re consistently running out of space, increasing your quota may help. Check your hosting provider’s email storage policies. For free email users, you may want to consider upgrading to a paid plan for more storage (e.g., Gmail, Outlook). For business email users, contact your IT team to expand your mailbox limit. 

Steps for email administrators

For business emails and workspaces, email administrators are the ones in charge of managing mailbox limits and other settings. Here are the steps email administrators need to take to help prevent and reduce the occurrences of SMTP Error 552 5.2.2 within the organization.

• Increase mailbox quotas. Adjust user limits to accommodate high-volume senders. Set notifications to warn users before they hit their limit.
• Enable automatic archiving. Move old emails to cloud storage or dedicated email archives as this keeps mailboxes clean without manual intervention.
• Monitor email storage reports. Identify users who frequently hit storage limits and offer proactive solutions. Review bounce logs to detect recurring SMTP 552 5.2.2 issues.
• Encourage best practices. Do take the time to educate employees on email cleanup strategies and attachment management.
• Consider upgrading hosting plans. If multiple users regularly max out their storage, it may be time to scale up email storage capacity.

Best practices to prevent SMTP Error 552 5.2.2 

Preventing “Mailbox Full” errors is easier than dealing with them after they occur. Follow these best practices to keep your inbox organized and ensure smooth email communication.

How Warmy helps prevent SMTP Error 552 5.2.2

While Warmy can’t control whether a recipient’s inbox is full, we can empower senders to optimize email deliverability to ensure your emails have the best chance of being received. Here’s how Warmy helps you avoid SMTP Error 552 5.2.2 and other deliverability issues:

Automated email warmup to establish and maintain a strong sender reputation

A poor sender reputation can increase the chances of your emails being deprioritized, delayed, or blocked entirely. Warmy automatically warms up your emails by:

• Sending emails gradually to establish trust with email providers and preventing ISPs from flagging your messages as spam.
• Mimicking human engagement with auto-replies, opens, and marking messages as important.
• Warming up using other providers that previously couldn’t be warmed up such as Mailchimp, Shopify, Klaviyo, etc.
• Allowing up to 5,000 warmup emails a day for consistent and optimized inbox placement

Advanced seed lists for locked in deliverability success

While traditional warmup involves lists of email addresses senders can use to warm up their domain and reputation, Warmy offers something groundbreaking. Our advanced seed lists are made up of genuine email addresses. Using Warmy’s advanced seed lists offer the following benefits:

• Authentic email interactions such as opening, scrolling, clicking, replying, and archiving, leading to an overall improvement in open rates and click rates
• In the event that an email does land in spam, it is removed and marked as important
• Results in better recognition by ISPs like Google, Microsoft, and Yahoo due to the seed lists organized per ISP
• Improved overall sender score and reputation, leading to higher inbox placement rate
• Provide a way to warm up email providers that other email warmup services cannot