Every time I select two photos from the gallery and mail them, the iPhone also adds two text attachments. How do I get it to stop that?
This is the fault of Microsoft Exchange and not specific to iOS.
This happens because Microsoft Exchange Server is reformatting messages sent through it.
The Exchange server insists that message text must always be first and attachments must always be last. As soon as the Exchange software sees one attachment in a message, it stops looking for text, and treats anything else in that message as an attachment. Any remaining text sections are converted into attachment sections, and given fake file names (like "ATT00001.htm").
At this time, there is no way to make the Exchange server stop turning text sections into attachment sections. The only workaround is to include attachments at the end of a message, after text and after any signatures.
The body of a message is shown incorrectly as an attachment if you try to use an application in an Exchange Server environment to send a message that includes attachments
Applies to Microsoft Exchange Server 2010 Enterprise, Microsoft Exchange Server 2010 Standard, Microsoft Exchange Server 2007 Enterprise Edition, Microsoft Exchange Server 2007 Standard Edition
This is a bug at Microsoft's end for Outlook accounts which use stock Mail app for iOS. There is absolutely no way in iOS to resolve this issue.
I avoid the ATT00001.txt file attachment by simply signing into my Outlook mail via the Other option. The steps to setup differ slightly across recent iOS releases. They are mentioned separately for recent iOS releases:
Under iOS 9, go to
Settings app -> Mail, Contact, Calendars -> Add Account -> Otherand enter appropriate information.
Under iOS 10 go to
Settings app -> Mail -> Add Account -> Otherand enter appropriate information.
Under iOS 11, go to
Settings app -> Accounts & Passwords -> Add Account -> Otherand enter appropriate information.