PHP mail() Error: Why Am I Getting \"Multiple or Malformed Newlines\"?

PHP Mail() Error: Navigating the 'Multiple or Malformed Newlines' Issue

Users have reported encountering the enigmatic "Multiple or malformed newlines found in additional_header" error when utilizing the PHP mail() function. Intriguingly, this error has emerged despite the absence of any discernable script modifications.

The inquiries have led to some startling revelations. The error appears to be server-specific, with 1and1 as the primary culprit. While the host's denial of responsibility casts doubt on their server configuration, suspicions linger that an undisclosed change might be at fault.

After exhaustive internet searches yielded limited results, a solution has emerged. The culprit lies in a recent PHP upgrade from 5.5.25-1 to 5.5.26. This upgrade addressed a security vulnerability in the mail() function, resulting in a strict prohibition against multiple newlines within the additional_headers parameter.

Solution:

1. Header Hygeine:

• Scrutinize headers for any instances of multiple newlines (rr, r

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