I’ve been having the same “Illegal address” error, but for me the problem can be isolated to having multiple BCC recipients: with zero or one BCC recipients, email is sent fine; with more than one, I get the error:
Error: Array ( [curl] => [Error] => Array ( [Type] => Sender [Code] => InvalidParameterValue [Message] => Illegal address ) [RequestId] => 9eddeb23-0ff4-11e7-8ecc-079760aaf245 )
I’m using the Gravity Forms plugin, so the BCC recipients are set on a form-by-form basis in a field as a comma-delimited list.
I turned on logging, and here’s an extract showing the error and its context:
1490296287 Start Logging
1490296310 wpses_mail [email protected] From: "Sender Name"
Bcc: [email protected],[email protected]
Content-type: text/html; charset=UTF-8
1490296310 extract headers
1490296310 add from "Sender Name"
1490296310 Line From: "Sender Name"
1490296310 Line Bcc: [email protected],[email protected]
1490296310 add Bcc [email protected],[email protected]
1490296310 Line Content-type: text/html; charset=UTF-8
1490296310 Error SimpleEmailService::sendEmail(): Sender - InvalidParameterValue: Illegal address
Request Id: 91a4a09e-0ffc-11e7-bd4b-87a61cff50bb
It looks like the problem is that it didn’t know to split the BCC recipients at the comma?