From a post at the German atnotes.de Forum:
Why does an attachment appears at the bottom of a Notes memo for one user, whereas it appears at the position it was created for other recipients?
It depends on the format of the mail address.
If I use Manfred Dillmann/IMD (which is my full hierarchical Notes name) as the address, the attachment is shown at the position where it was placed during the composing of the mail.
If I use my internet address email@example.com, the mail looks like that on the recipients side.
The attachment was moved to the bottom of the mail.
Why does that happens?
Because of the use of an internet address, Notes converts the mail to a ‚real internet mail‘ – which means: to a multipart MIME mail. You can verify this for yourself by looking at the documents properties of that mail. You will find a Notes field ‚$NoteHasNativeMIME‘ with a value set to ‚1‘. And please take a look at the ‚Body‘ fields, too.
Attachments in MIME mails will always be displayed at the bottom of the mail within the Notes Client.