EDIT: Maybe your class for sending emails has an option for HTML emails and then you can use <br />
1) Double-quotes
$output = "Good news! The item# $item_number on which you placed a bid of \$ $bid_price is now available for purchase at your bid price.\nThe seller, $bid_user is making this offer.\n\nItem Title : $title\n\nAll the best,\n $bid_user\n$email\n";
If you use double-quotes then \n will work (there will be no newline in browser but see the source code in your browser - the \n characters will be replaced for newlines)
2) Single quotes doesn't have the effect as the double-quotes above:
$output = 'Good news! The item# $item_number on which you placed a bid of \$ $bid_price is now available for purchase at your bid price.\nThe seller, $bid_user is making this offer.\n\nItem Title : $title\n\nAll the best,\n $bid_user\n$email\n';
all characters will be printed as is (even variables!)
3) Line breaks in HTML
$html_output = "Good news! The item# $item_number on which you placed a bid of <br />$ $bid_price is now available for purchase at your bid price.<br />The seller, $bid_user is making this offer.<br /><br />Item Title : $title<br /><br />All the best,<br /> $bid_user<br />$email<br />";
- There will be line breaks in your browser and variables will be replaced with their content.