i can easily make the changes i need with this

Set-ADUser -Identity $sam -Add @{ProxyAddresses = $proxyaddresses} -Server $servername

however, i like to have the option of a way to do this without RSAT in case I'm on a computer without it installed.

i have seen plenty of times that people use this:

https://www.reddit.com/r/PowerShell/comments/2jiqcj/script_for_adding_proxyaddresses_to_accounts/

# https://docs.microsoft.com/en-us/previous-versions/tn-archive/ee156515(v=technet.10)
# https://docs.microsoft.com/en-us/windows/desktop/adsi/the-putex-method
[int] $ADS_PROPERTY_CLEAR = 1
[int] $ADS_PROPERTY_UPDATE = 2
[int] $ADS_PROPERTY_APPEND = 3
[int] $ADS_PROPERTY_DELETE = 4

# Derive user DN in whatever method you prefer        
# Delete, Append, Update - Take your pick
$ADuser = [ADSI]"LDAP://Contoso-DC-08/$($userAccount.DistinguishedName)"          
$ADuser.PutEx($ADS_PROPERTY_DELETE, "proxyAddresses", @("smtp:[email protected]"))
$ADuser.PutEx($ADS_PROPERTY_APPEND, "proxyAddresses", @("SMTP:[email protected]"))

# Commit changes to AD User Object
$ADuser.SetInfo()

but no matter which way i do it, i just end up with this!

Exception calling "PutEx" with "3" argument(s): "Unspecified error
"
At C:\path\to\script.ps1:214 char:1
  $ADuser.PutEx($ADS_PROPERTY_APPEND, "proxyAddresses", @($proxyaddress ...
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
      FullyQualifiedErrorId : CatchFromBaseAdapterMethodInvokeTI

and i can't for the life of me figure out why... Q_Q

any help would be greatly appreciated