Using Send-MailMessage with multiple recipients

I have a script that sends out an email to a large number of distribution lists as a final steps. In testing, if I send it to one person it works fine. The issue comes in when I am trying to send to multiple recipients. I have looked at the Send-MailMessage help topic and it expects a string[] for the -To field. I would think that I could do something like this:

$sTo = “group1@mycompany.com,"group2@mycompany.com","group3@mycompany.com"

or:

$sTo = “group1@mycompany.com;group2@mycompany.com;group3@mycompany.com

or even:

[string[]]$sTo = “group1@mycompany.com,"group2@mycompany.com","group3@mycompany.com"

But all of them generate the same error:

Cannot process argument transformation on parameter ‘msgrecipient’. Cannot convert value to type System.String.

I have tried putting the names into an array and then using .Split or .ToString, but still cannot seem to get the syntax correct. Any suggestions would be welcome.

String[] is a string array, which is your first example:

$sTo = "group1@mycompany.com","group2@mycompany.com","group3@mycompany.com"

The following works fine for me (Office 365 SMTP):

$cred = get-credential

$params = @{
    To = 'rob.simmers@email1.com', 'rs@email2.com'
    From = 'rob.simmers@email1.com' 
    Subject = 'Test Email'
    Body = 'Testing for Powershell.org'
    BodyAsHtml = $true
    SmtpServer = 'smtp.office365.com' 
    UseSsl = $true
    Credential = $cred 
    Port = 587
}

Send-MailMessage @params

Thanks, this seems to work in testing. I still am unsure why what I was trying wouldn’t work.