To: test@example.com From: test@example.com Subject: HTML with split tag Message-ID: <8259dd8e-2293-8765-e720-61dfcd10a6f3@example.com> Date: Sat, 30 Dec 2017 19:12:38 +0100 User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:59.0) Gecko/20100101 Thunderbird/59.0a1 MIME-Version: 1.0 Content-Type: text/html; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-GB HTML part. Now comes the tag ShouldFindThisAgain The following should *not* be found: ShouldNotFind AcrossLines ShouldFind AcrossLines