this is easier

internal/configurations/configuration.ps1

@@ -8,7 +8,7 @@ Register-PSFConfigValidation -Name validation.LogFileComparisonValidations -Scri
 $EmailValidationSb = {
     param ([string]$input)
     $EmailRegEx = "^\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*$"
-    if ($input -match $EmailRegEx) {
+    if (($input -match $EmailRegEx) -or -not ($input) ) {
         [PsCustomObject]@{Success = $true; value = $input}
     } else {
         [PsCustomObject]@{Success = $false; message = "does not appear to be an email address - $input"}
@@ -235,7 +235,7 @@ Set-PSFConfig -Module dbachecks -Name domain.domaincontroller -Value $null -Init
 
 # email
 Set-PSFConfig -Module dbachecks -Name mail.failurethreshhold -Value 0 -Initialize -Description "Number of errors that must be present to generate an email report"
-Set-PSFConfig -Module dbachecks -Name mail.smtpserver -Value $null -Validation string -Initialize -Description "Store the name of the smtp server to send email reports"
+Set-PSFConfig -Module dbachecks -Name mail.smtpserver -Value $null -Initialize -Description "Store the name of the smtp server to send email reports"
 Set-PSFConfig -Module dbachecks -Name mail.to -Value $null -Validation validation.EmailValidation -Initialize -Description "Email address to send the report to"
 Set-PSFConfig -Module dbachecks -Name mail.from  -Value $null -Validation validation.EmailValidation -Initialize -Description "Email address the email reports should come from"
 Set-PSFConfig -Module dbachecks -Name mail.subject  -Value 'dbachecks results' -Validation String -Initialize -Description "Subject line of the email report"