Step 1 - Set variables for mail options. 
  $sqlServer = 'YourServerName'
  $accountName = 'dbMailDefaultAcct'
  $accountDescription = 'Default dbMail Account'
  $originatingAddress = "$sqlServer@yourDomain.com"
  $replyToAddress = 'DO_NOT_REPLY@yourDomain.com'
  $smtpServer = 'smtpServer.yourDomain.com'
  $profileName = 'dbMailDefaultProfile'
  $profileDescription = 'Default dbMail profile'
 
. Step 2 - Load the SMO assembly and create the server object, connecting to the server
  [System.Reflection.Assembly]::LoadWithPartialName('Microsoft.SqlServer.SMO') | Out-Null
  $server = New-Object 'Microsoft.SqlServer.Management.SMO.Server' ($sqlServer)
 
Step 3 - Configure the SQL Server to enable Database Mail.
  $server.Configuration.DatabaseMailEnabled.ConfigValue = 1
  $server.Configuration.Alter()
 
Step 4 - Alter mail system parameters if desired, this is an optional step.
  $server.Mail.ConfigurationValues.Item('LoggingLevel').Value = 1
  $server.Mail.ConfigurationValues.Item('LoggingLevel').Alter()
 
Step 5 - Create the mail account. 
# ArgumentList contains the mail service, account name, description, 
# display name and email address.
  $account = New-Object -TypeName Microsoft.SqlServer.Management.SMO.Mail.MailAccount `
   -Argumentlist $server.Mail, $accountName, $accountDescription, $sqlServer, $originatingAddress 
  $account.ReplyToAddress = $replyToAddress 
  $account.Create()
 
Step 6 - Set the mail server now that the account is created.
  $account.MailServers.Item($sqlServer).Rename($smtpServer)
  $account.Alter()
 
Step 7 - Create a public default profile. 
# ArgumentList contains the mail service, profile name and description.
  $mailProfile = New-Object -TypeName Microsoft.SqlServer.Management.SMO.Mail.MailProfile ` 
   -ArgumentList $server.Mail, $profileName, $profileDescription
  $mailProfile.Create()
 
Step 8 - Associate the account to the profile and set the profile to public
  $mailProfile.AddAccount($accountName, 0)
  $mailProfile.AddPrincipal('public', 1)
  $mailProfile.Alter()
 
Step 9 - Configure the SQL Agent to use dbMail.
  $server.JobServer.AgentMailType = 'DatabaseMail'
  $server.JobServer.DatabaseMailProfile = $profileName
  $server.JobServer.Alter()