Solution

1. Stop Confluence

2. Back up your Confluence database

3. Run the following query on the database: 

   SELECT * FROM BANDANA WHERE BANDANAKEY = 'atlassian.confluence.smtp.mail.accounts';

4. Find the following in the BANDANAVALUE:

   <property name="mail.smtp.timeout" value="10000"/>

   and

   <property name="mail.smtp.connectiontimeout" value="10000"/>

5. Use SQL's REPLACE function to increase the values
   EXAMPLE:

   UPDATE BANDANA
      SET BANDANAVALUE = replace(BANDANAVALUE,'<property name="mail.smtp.connectiontimeout" value="10000"/>','<property name="mail.smtp.connectiontimeout" value="20000"/>')
    WHERE BANDANAVALUE LIKE '%mail.smtp.connectiontimeout%';
   
   
   UPDATE BANDANA
      SET BANDANAVALUE = replace(BANDANAVALUE,'<property name="mail.smtp.timeout" value="10000"/>','<property name="mail.smtp.timeout" value="20000"/>')
    WHERE BANDANAVALUE LIKE '%mail.smtp.timeout%';

   
   

   For MS SQL the update statements are:

   UPDATE BANDANA
      SET BANDANAVALUE = CAST(REPLACE(CAST(BANDANAVALUE as nvarchar(max)),'<property name="mail.smtp.timeout" value="10000"/>','<property name="mail.smtp.timeout" value="20000"/>') as ntext) 
    WHERE BANDANAVALUE LIKE '%mail.smtp.connectiontimeout%';
   
   UPDATE BANDANA
      SET BANDANAVALUE = CAST(REPLACE(CAST(BANDANAVALUE as nvarchar(max)),'<property name="mail.smtp.connectiontimeout" value="10000"/>','<property name="mail.smtp.connectiontimeout" value="20000"/>') as ntext) 
    WHERE BANDANAVALUE LIKE '%mail.smtp.timeout%';
   

   Also note:  If email settings are updated, the settings will revert to the default.  You will need to reproduce these steps after the change has been made.

6. Restart Confluence

1. Stop Confluence.

2. Move (don't copy) the following files from <confluence-install>\confluence\WEB-INF\lib to <confluence-install>\lib:

com.sun.activation_jakarta.activation-x.x.x.jar
com.sun.mail_jakarta.mail-x.x.x.jar

   (x.x.x. represents the version numbers on the jar files in your installation)
   
   Don't leave a renamed backup of the jar files in \confluence\WEB-INF\lib. Even with a different file name, the files will still be loaded as long as it remains in the directory.

3. Edit the <confluence-install>\conf\server.xml file and add the following at the end of the Confluence <context> tag, just before </Context>.
   Note: you're editing the <context> tag that contains the Confluence context path, not the one that contains the Synchrony context path.

   <Resource name="mail/GmailSMTPServer"
       auth="Container"
       type="javax.mail.Session"
       mail.smtp.host="smtp.gmail.com"
       mail.smtp.port="465"
       mail.smtp.auth="true"
       mail.smtp.user="yourEmailAddress@gmail.com"
       password="yourPassword"
       mail.smtp.starttls.enable="true"
       mail.transport.protocol="smtps"
       mail.smtp.socketFactory.class="javax.net.ssl.SSLSocketFactory"
   />
   

4. Restart Confluence.

5. Go to Administration  > General Configuration > Mail Servers.

6. Select either Edit an existing configuration, or Add a new SMTP mail server.

7. Edit the server settings as necessary, and set the JNDI Location as:

    java:comp/env/mail/GmailSMTPServer
   

   
   Note that the JNDI Location is case sensitive and must match the resource name specified in server.xml.

8. Save your changes and send a test email.