Out-of-office automatic email replies are useful to let people know that you aren't viewing or responding to your emails because you are on vacation or away for any other reason. Every email provider worth its salt has the option somewhere, including Outlook. If you use Outlook to manage other emails like your Gmail or iCloud accounts, you should go directly to the source to set up an out-of-office reply (i.e. log in to Gmail to set up automatic replies for that account).
There are many apps that will manage your email accounts besides the iOS Mail app - Thunderbird, Outlook and Gmail will all do the job, to name a few. Outlook is popular with a lot of businesses, so if your work email is managed by Outlook you might want to add your other emails just to be able to access them all in one place. Or maybe you prefer the Outlook interface to that of Mail.
Microsoft continues to update and improve the Outlook email app for Apple Watch. Recently owners of the watch have been able to enjoy replying to emails without ever looking at the iPhone. In addition to using Siri to reply to email, Outlook 1.3.7 users can quickly check their Inbox or calendar from a glance. The app also pushes interactive, custom notifications to the Apple Watch.
The official Outlook email client has arrived on iOS. This all-in-one free app provides access to Microsoft Exchange, Office 365, Outlook.com, iCloud, Gmail and Yahoo Mail. Calendar and attachment access is fully integrated, with easy access to Microsoft OneDrive, Dropbox and other accounts.
Microsoft Outlook is based heavily on the former Acompli app, which the company acquired in December. Like Acompli, Outlook promises to unify calendar, contacts and attachments with email to improve mobile productivity. To top it off, Quick Filters and recent contacts make it easy to search for emails, meetings and files.