After having updated OS X to the latest version (currently version 10.10.4), you may find that while Mail will launch and display messages, it may not send or receive new ones. In some cases this problem is only in one direction, where you might be able to send messages but not receive them or perhaps receive messages but not be able to send them. These behaviors in Mail might seem a bit perplexing, but generally can be fixed with a few steps.

Isolate the problem

First go to Mail’s Connection Doctor utility (in the Window menu) to see if the issue is isolated to one account, and specifically to both the account’s outgoing and incoming servers. If one server is working properly, then your account with the email provider is working properly and the issue at hand is only with your server configuration.

On the other hand, if you cannot connect to either your incoming or outgoing servers, then even though this could still be a configuration issue, chances are the problem is with a setting in your account. Your best bet at this point is to contact your service provider to determine if your account is still active, or if anything has changed.

Look up your service provider’s settings

Unfortunately Mail may be configured to change connection settings dynamically, which in addition to being the root cause of some Mail problems, may makes the current settings in Mail unreliable to use as a reference for what ought to be correct for your account. Therefore, contact your service provider to see what address, port, and security options are required for your account. Most e-mail accounts will use some combination of either IMAP or POP3 services with an SSL option, along with a service port, and an authentication type, so these should be available on support pages or by calling help lines.

In some cases, providers may give you two or more possible configurations, such as one for SSL usage, and another that does not require SSL. In these cases, mark down the configurations for both.

Remove SMTP server keychain entries

Since you are having troubles we will start the Mail configuration from scratch, so while it is a somewhat generic approach, we will start by removing all keychain entries for your outgoing mail server:

1. Launch Keychain Access (from the Applications > Utilities folder).
2. Search for your SMTP server (ie, mail.example.com, or smtp.example.com).
3. Select and delete the keychain password entries that show.

Delete and re-add SMTP servers

Go to Mail’s preferences and then click the Accounts section. In here, select your account and then select the Account Information Tab. Then click the Outgoing Mail Server menu and choose the option to edit the list. From here, select the current outgoing server and click the minus button to delete it.

Now click the plus button to re-add your server, and perform the following actions:

1. Enter the server description.
2. Enter the server URL.
3. Click “Advanced” and enter your server port number (start with your non-SSL configuration, if available).
4. Choose “No Password” for your authentication.

Click OK to save the settings and close the configuration window; then try sending your message. Without a password set, expect the attempt to fail, but also expect it to have attempted the connection. When you get the same outgoing server error message, read the message to see if you get a specific error such as “relaying denied,” “authentication error,” or anything. The specifics do not matter, but only that you have established a connection and have been refused.

At this point, go back to the SMTP server list, and in the Advanced tab for your SMTP server, change the authentication scheme to Password, followed by supplying your account’s username and password.

Save the settings and again try to send your message using this account. If all is working, you should be able to send the message; however, if not then you can try several small tweaks to get it going:

1. Check the box to allow insecure authentication.
2. Check or uncheck “Use SSL” and try again.
3. Change your port from the non-SSL one to the one for SSL connections.

Note that even though some providers specify a port for SSL and non-SSL connections, these may sometimes work interchangeably. This unfortunately means you have more combinations of these settings to try, but at least one combination should work.

Managing invalid certificates

In some cases your account may use a certificate that Mail claims is invalid, or perhaps may not be trusted. In these cases, your provider’s server URL may have changed. For instance, it might have been “smtp.example.com,” but then changed to “mail.example.com,” which can trigger this error. At times, these URL changes may simply be cosmetic as they will ultimately connect to the same server, but the change nevertheless may cause small issues.

To get around this problem, first try ensuring your server’s URL is correct per your provider’s provided configurations. That means, if you have been using “smtp.example.com” but are given “mail.example.com” as your server to use, then use the latter. If the certificate warnings continue, then you can contact your provider to see what might be the problem. Alternatively, you can try bypassing the certificate if you know the server URL you are using is correct. You can test this using Apple’s Network Utility program:

1. Open Network Utility (in the Applications > Utilities folder).
2. Go to the Traceroute tab.
3. Enter your mail server URL.
4. Click the Trace button.

In the output, a list of servers will be shown, which are the individual hops your connection makes as you traverse the internet to get to your provider’s server. For each hop, you will see the server used, along with its IP address, and then some response time measurements (in milliseconds). If you see the last servers as belonging to your provider (ie *.example.com), then the server you are using is resolving to your provider’s domain (that on the certificate) and can likely be trusted.

At this point, if you still are experiencing invalid certificate warnings, you can change its settings from “Use System Defaults” to “Always Trust” so it will not show again.

Preventing future problems

Finally, one thing to keep in mind is this issue may crop up again in the future if your provider changes its mail server settings; however, this is relatively rare and providers usually issue fair warning before taking such actions. On the other hand, Mail has some settings that will track and attempt to make changes to your configuration to ensure you are connected. Unfortunately this does not seem to work properly all the time, and may cause Mail to change its port number and authentication settings to something that does not work. To prevent this, turn off this feature for both incoming and outgoing servers:

1. Go to Mail’s preferences and click “Accounts.”
2. Select your account and click the Advanced tab.
3. Uncheck the option at the top to automatically detect and maintain account settings.
4. Go to the Account Information tab.
5. Select Edit SMTP Server List from the Outgoing Mail Server menu.
6. Select your SMTP server.
7. Click “Advanced” and similarly disable the automatic detection of account settings.