Guide Email

How to fix email that will not send

The most common reasons an email client refuses to send, checked in the order most likely to find the fault.

iFastHosting Support Team Updated 26 August 2026 7 min read Intermediate

Mail that will not send almost always comes down to the outgoing server settings — a mail client's incoming and outgoing servers are two separate configurations, and receiving mail working fine tells you nothing about whether the outgoing side is set up correctly.

1. Check the outgoing server requires authentication

The single most common cause. Sending mail through your domain's own server requires the same username and password as receiving it — this is not optional, and it is a separate setting from the incoming server's login in most mail apps, sometimes tucked away under an "advanced" or "outgoing server" tab that is easy to miss during initial setup.

This is the setting people miss most often

An account can be set up correctly in every other respect, receive mail perfectly, and still fail to send purely because "requires authentication" or "use same settings as incoming" was left unticked on the outgoing server. Check this first before anything else on this list.

2. Check the outgoing port and encryption match

Port 587 expects STARTTLS; port 465 expects SSL/TLS from the start. Mismatching the port and encryption type produces a connection failure that looks identical to a wrong password in many mail apps. See which email ports to use for the full reference.

3. Check the outgoing server hostname

Confirm it matches exactly what your control panel shows — a single mistyped character produces "server not found" rather than a spelling-specific error. Copy it directly from your control panel rather than retyping it from memory.

4. Check you have not hit a sending limit

Shared hosting mailboxes have a limit on how many messages can be sent within a given period. If you have recently sent a large batch, this may be the cause — see how many emails you can send per hour.

5. Check the mailbox is not full

Some mail servers refuse outgoing mail from a mailbox that has reached its storage quota, on the basis that sent mail is also stored and counted. See what a mailbox quota is.

6. Check for a message stuck specifically because of its content

A very large attachment can exceed a server's maximum message size and fail to send while smaller messages go through without issue. If only large messages are affected, this is the likely cause — check your control panel or provider documentation for the maximum message size on your plan.

7. Check whether the network itself is blocking the connection

Some networks — particularly some public Wi-Fi and certain corporate or mobile networks — block outbound connections on mail ports as a security measure. If sending fails consistently on one specific network but works fine on another, such as switching from office Wi-Fi to mobile data, this is the likely explanation rather than anything wrong with the mailbox itself.

Working through it systematically

Note the exact error message
Mail apps usually show a specific error code or description when sending fails — this often points directly at authentication, connection, or size as the category of problem.
Test sending a very small message
A short message with no attachment rules out a size-related cause and isolates the problem to authentication, server settings, or the network.
Try from a different network
Switching from Wi-Fi to mobile data, or vice versa, rules network blocking in or out.
Re-enter the outgoing server settings from scratch
Rather than editing an existing configuration, removing and re-adding the account with settings copied fresh from your control panel eliminates the possibility of a small, hard-to-spot error in the existing setup.

Reference: correct outgoing settings

Field	Value
Outgoing server	Shown in your control panel
Port	587 (STARTTLS) or 465 (SSL/TLS)
Authentication	Required — same username and password as incoming
Username	The full email address

If sending fails with an error specifically about the login or password rather than a connection error, fixing authentication failed errors covers that more specific case in detail.

Messages stuck in the outbox rather than failing outright

A message stuck in an app's outbox, neither sending nor showing a clear error, usually means the app keeps retrying a connection that is failing quietly in the background rather than reporting the failure to you directly. Check the account's connection status within the app first — most show a small status indicator or a specific "cannot connect" notice if you look at the account settings rather than just the message list. Removing and re-adding the account, with settings copied fresh from your control panel, usually clears a stuck outbox faster than waiting for retries to eventually succeed or fail with a visible error.

Sending works from one device but not another

If the same mailbox sends fine from a computer but not from a phone, or the reverse, the fault is specific to the failing device's configuration rather than the mailbox or hosting account — a mailbox does not have separate sending permissions per device. Compare the outgoing settings on both devices side by side, field by field, since a working device gives you a known-correct reference to check the failing one against.

One provider working and another failing points at authentication, not the network

If mail sends successfully through one linked account but not another on the same device and the same network, a network-level block can be ruled out — the difference has to be in that specific account's settings, most often the outgoing server's authentication requirement.

Checking the send actually failed, rather than just being slow

Occasionally what looks like a sending failure is simply a delay on the receiving end rather than anything wrong with your setup — a busy destination mail server can take longer than usual to accept a connection. Before assuming the worst, wait a few minutes and check whether the message eventually left the outbox, and confirm with the recipient whether it arrived, before working through the full list of checks above.