The two most popular methods that our products use to send email messages are
- PHP mail() function
Some products use both methods, some just one of them. Please contact us if you need information which of the methods the script you have uses.
Often hosting companies have limitations when it comes to send emails using PHP. This is understandable as they want to protect themself from getting the web servers blacklisted if their clients auto send messages to thousands and even millions of email addresses. Before we can troubleshoot email sending problems we need to know if your hosting company supports PHP mail() function and SMTP or if they require some special code to be used.
Once an email is sent out the script is not responsible for routing it between servers.
If emails are being sent and then received by some servers but not others that means that recipient server where messages are not received rejects the incoming email messages. We would advise you to contact server administrator and check if there is not some firewall or spam filter working on the recipient server. Or the sender's server IP address may be blocked by the recipient server.
Furthermore the script does not know what the server it sends email to is - Linux or Windows and does not make any difference in sending the email. Email message is sent to every email account specified.
What puts an email message into a spam box is the recipient email server. This is how email sending works in general
1) the script is hosted on your server
2) the script uses PHP mail() or SMTP method to send emails
3) when email is sent the message itself is being sent out from your server
4) the message is then routed between all the servers in the network
5) message arrives in your mail box hosted on the recipient server
That recipient server decides where to deliver the message based on the rules set - inbox, spam box, block the message, some specific folder, etc.. The script is not responsible for where email message arrives. It's the recipient server which decides where to deliver each message received. If you receive an email message in your spam box you should ask your email provider what the reason for this is and if they have any automatic rules set to filter incoming email and mark it as spam.