I received a message with a PDF attachment of 20 MB which isn't shown as attachment in the message list (the paper clip icon is missing).
Looking at the source of the message, the structure looks like this:
Content-Type: multipart/alternative; boundary="Apple-Mail=_E26C74AC-94C5-415E-BA83-E2830C22D7E4"
[... now the body: ...]
--Apple-Mail=_E26C74AC-94C5-415E-BA83-E2830C22D7E4 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=utf-8
[... Text part ...]
--Apple-Mail=_E26C74AC-94C5-415E-BA83-E2830C22D7E4 Content-Type: multipart/mixed; boundary="Apple-Mail=_BD2C8A48-FD16-4995-B226-8C85EEDEA387"
--Apple-Mail=_BD2C8A48-FD16-4995-B226-8C85EEDEA387 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=utf-8
[... HTML part ...]
--Apple-Mail=_BD2C8A48-FD16-4995-B226-8C85EEDEA387 Content-Disposition: inline; filename="Nordkap Recall Teil 1.pdf" Content-Type: application/pdf; x-mac-hide-extension=yes; x-unix-mode=0644; name="Xxxxxxx Xxxxxx Teil 1.pdf" Content-Transfer-Encoding: base64
[... b64-encoded attachment ...]
--Apple-Mail=_BD2C8A48-FD16-4995-B226-8C85EEDEA387 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=utf-8
[... another HTML part (?!) ...]
--Apple-Mail=_BD2C8A48-FD16-4995-B226-8C85EEDEA387--
--Apple-Mail=_E26C74AC-94C5-415E-BA83-E2830C22D7E4--
Cheers,
Michael Heydekamp Co-Admin freexp.de Düsseldorf/Germany