Doc Summary
Introduction #
As email can have lots of different issues when configured incorrectly, we’ve put the most common ones in this doc and how to fix these issues. Having an issue not listed in this doc? Contact us anytime.
Mailbox Full #
A mailbox full issue happens when an email account has reached its storage limit and can no longer accept new incoming messages. When this happens, email delivery to that specific mailbox is affected immediately.
This can apply to any ProRedLine service that includes email functionality, including both Email Hosting and Web Hosting.
What Happens When a Mailbox Is Full #
Once a mailbox reaches its allowed storage limit, new incoming emails may no longer be delivered to that account. In many cases, the sender will receive a bounce message explaining that delivery failed because the mailbox is full.
Email is not normally held until space becomes available again. Instead, delivery usually fails at the time the message is sent to the mailbox.
How to Recognize the Problem #
A full mailbox often becomes visible through delivery failures rather than through the mailbox itself. Common signs include bounce-back messages mentioning storage limits, missing incoming messages, or reports that email is not arriving even though other parts of the service appear to be working normally.
In many cases, the mailbox owner may still be able to log in and review the account, but new mail will not continue arriving until storage is freed.
Where to Check Mailbox Usage #
Mailbox usage can be reviewed in cPanel through the Email Accounts area. There, you can see how much space each email account is currently using and compare that against the assigned mailbox limit.
This is the easiest way to confirm whether the problem is caused by the mailbox reaching its allowed storage capacity.
Common Causes #
Mailboxes usually become full over time because of stored content rather than one single message. Common causes include large attachments, old emails that were never removed, growing Sent folders, accumulated spam or junk mail, and Trash folders that still contain deleted messages.
It is also important to remember that deleting an email does not always free space immediately if the message is still stored in Trash or another folder.
How to Resolve It #
The usual solution is to reduce the amount of data stored in the affected mailbox. This can often be done by deleting old emails, emptying Trash and Junk folders, removing messages with large attachments, or archiving older messages outside the mailbox if needed.
Once enough space has been freed, incoming mail can usually be received again without further action.
Adjusting Mailbox Limits #
If needed, the mailbox limit itself may also be increased, provided the hosting package allows it and enough total package storage is still available. However, increasing the limit is only useful if the overall package has enough storage capacity left, since mailbox usage still contributes to the total storage of the hosting service.
Preventing the Problem #
Mailbox full issues are usually preventable with regular cleanup and occasional usage checks. Keeping an eye on mailbox size, removing unnecessary attachments, and clearing Junk or Trash folders periodically can help prevent delivery interruptions in the future.
Sending Email Errors #
A sending email error occurs when an email cannot be sent successfully from your mailbox. In most cases, this means the message is being blocked or rejected before it can be delivered to the next mail server.
These problems are often related to SMTP configuration, authentication, or connection issues rather than to the recipient itself.
What SMTP Is #
SMTP stands for Simple Mail Transfer Protocol. It is the system used to send outgoing email from your mailbox to other mail servers.
If SMTP is not working correctly, outgoing mail will fail even if receiving email still works normally.
Common Signs of a Sending Error #
Sending problems can appear in different ways. Common signs include error messages when trying to send, emails remaining stuck in the outbox, immediate send failures, or bounce-back messages with technical error codes.
These symptoms usually point to a sending or authentication issue rather than a general mailbox problem.
Common Causes #
One of the most common causes is incorrect SMTP configuration in the email client. If the outgoing server details are wrong, the connection may fail before the email is sent. This includes using the wrong SMTP hostname, port, encryption method, or missing authentication settings.
Incorrect login credentials are another frequent cause. SMTP requires authentication, which means the full email address and the correct password must be entered exactly as required. If the username, password, or formatting is wrong, the server may reject the login attempt.
Another common issue is using the wrong port or encryption combination. If the selected port does not match the expected SSL or TLS configuration, the client may be unable to establish a valid connection.
In some cases, the problem is related to the network rather than the mailbox itself. Certain internet providers, public networks, or business networks may restrict SMTP traffic. If sending works on one network but fails on another, the issue may be caused by network-level blocking.
Mailbox-related conditions can also affect sending. For example, problems may occur if the account is suspended, if storage limits have been reached, or if the mailbox was created very recently and the setup is not yet fully active everywhere.
Secure SMTP at ProRedLine #
At ProRedLine, SMTP sending requires authentication and secure connections. Unauthenticated or plain SMTP sending is not supported.
This means the mail client must be configured with the correct sending settings and valid mailbox credentials before sending will work properly.
Reading Error Messages #
SMTP-related error messages can often point directly to the type of problem involved. Messages such as authentication failed, connection timed out, or relay access denied usually indicate a configuration, credential, or permission issue.
Although the exact wording can vary depending on the email client, these errors are often enough to narrow down whether the problem is related to login details, connectivity, or server access rules.
What to Check First #
When sending email fails, the most useful first steps are usually:
- recheck the SMTP settings in the email client
- verify the full email address and password
- try sending through webmail to confirm whether the mailbox itself works
- test from a different network if a connection problem is suspected
If sending works in webmail but not in your mail app, the issue is usually in the client configuration rather than in the mailbox itself.
Send Emails Going to Spam #
If an email is delivered to a spam or junk folder, it means the receiving mail provider did not fully trust the message, even though it was technically accepted and delivered. In other words, the email reached the destination server, but it was filtered away from the main inbox.
This is an important distinction, because it means the issue is not usually that the message failed to send. Instead, the problem is that the receiving side considered the message suspicious enough to place it in spam.
Why This Happens #
Spam filtering is controlled by the receiving provider, not by ProRedLine. Services such as Gmail, Outlook, Yahoo, and other mail providers decide for themselves whether a message should go to the inbox, spam folder, or be rejected.
That decision is usually based on a combination of factors rather than one single setting. Common reasons include:
- missing or incorrect SPF, DKIM, or DMARC records
- a new or low-reputation domain
- suspicious message content
- high-volume or unusual sending patterns
- forwarding through external providers
In many cases, more than one factor is involved.
Check Authentication First #
The first thing to review is email authentication. Correct SPF, DKIM, and DMARC configuration is one of the most important parts of improving trust in outgoing email.
You should verify that:
- an SPF record exists and is correct
- DKIM is enabled and valid
- a DMARC record is present
These settings can be reviewed in cPanel through Email Deliverability. If authentication is missing or misconfigured, the chance of spam placement increases significantly.
Content Can Also Trigger Spam Filters #
Even when authentication is correct, the content of the message can still cause filtering issues. Messages may be treated as suspicious if they use misleading subject lines, contain excessive links or images, rely on spam-like wording, or have poor formatting or broken HTML.
In general, messages are more trusted when they are clear, simple, and professionally formatted.
Reputation Matters #
A domain that has only recently started sending email has little or no established reputation. Because of that, messages from new domains are more likely to be filtered more aggressively at first.
Reputation usually improves over time when email is sent consistently, authentication remains correct, complaint rates stay low, and messages are not being marked as spam by recipients. This process takes time and cannot be forced immediately.
Forwarding Can Make It Worse #
Forwarded email is more likely to end up in spam than directly delivered email. This is because forwarding can cause authentication problems at the final destination, especially with SPF.
For that reason, direct delivery is usually more reliable than forwarding whenever possible.
What You Can Do #
If your emails are going to spam, the best steps are usually:
- verify SPF, DKIM, and DMARC
- avoid bulk or inconsistent sending behaviour
- use clear sender names and recognisable email addresses
- keep the email content simple and professional
- avoid unnecessary forwarding where possible
- ask recipients to mark legitimate emails as not spam
That last step can be especially helpful when dealing with mailbox providers that learn from recipient behaviour.
Important Note #
Because spam filtering happens on the recipient side, ProRedLine cannot override the decision made by another mail provider. The goal is therefore not to “force” inbox placement, but to improve the trust signals around your domain and your messages so they are more likely to be accepted as legitimate over time.
Emails During Downtime at ProRedLine #
At ProRedLine, all email services are hosted on secure and continuously monitored servers. If your mail server (for example, Main Server 1) becomes temporarily unavailable, incoming messages are not lost.
Most sending mail systems follow the SMTP retry standard, which ensures that emails are safely queued until the server is back online. When delivery fails, the sender’s mail server will:
- Queue the message instead of discarding it.
- Retry delivery automatically at regular intervals (usually every 15 to 60 minutes).
- Continue retrying for up to 24 to 48 hours, depending on the sender’s configuration.
Such temporary interruptions may occur during scheduled maintenance or rare service incidents, but these periods are typically short and are resolved well within 24 hours, in fact, none have ever approached that duration.
As soon as the ProRedLine mail server becomes reachable again, all queued messages are delivered automatically. Only if downtime exceeds the retry period (typically more than two days) will the sender receive a Delivery Failed or Undeliverable notice.
Conclusion #
Temporary downtime, such as maintenance or short service incidents, does not result in permanent email loss. Incoming messages remain safely queued on the sender’s system and are delivered automatically once service is restored. Extended outages beyond two days are extremely unlikely thanks to ProRedLine’s continuous uptime monitoring and redundancy systems.
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