Why you can’t force Outlook to send email in HTML
I’ve had several emails recently asking where to find the setting to force Outlook to always send in HTML format, even in reply to a message received in plain text. Sorry to disappoint, but it doesn’t exist, and for a good reason: Outlook replies in the same format as the original message, so you don’t reply in HTML to someone whose client doesn’t understand it.
If someone sends you mail in plain text it could be for a few reasons – because their client doesn’t understand HTML, or because they prefer plain text – whereas if you receive an email in HTML format, you can be pretty sure the sender’s mail client understands HTML and you can reply in the same format without any problem. In short, receiving a plain text mail permits no inference about whether the sending mail client can or can’t understand HTML.
It might be considered discourteous or disrespectful to reply in HTML
HTML and MIME formats were never in the original email specification, but were later additions, and despite what many people think there’s a sizable number of email clients still in use that can’t understand HTML. HTML doesn’t automatically get converted to plain text at the receiving end, as some people believe. The text of the message is actually sent twice, once in plain text and then again in HTML, both wrapped in a MIME envelope inside the email message, and it’s left to the receiver’s email client to decide which version to display.
If you send an HTML mail to one of these older mail clients that only understands plain text, it will display the MIME envelope, the plain text and the source code of the HTML version all at once, which will look like gibberish to many people and cause them to give up and delete your message.
Whether the recipient is using an older email client, or they’ve deliberately chosen to send plain text, it might be considered discourteous or disrespectful to reply in HTML. Imagine you’re in Italy and can speak both German and Italian: someone approaches you in the street and asks “Dove si trova la stazione, per favore?” Surely you’d reply in Italian?
If you’re sure the sender’s mail client can accept HTML, and that they won’t mind you changing the format of your conversation, then it’s easy enough to do as the tools are all on the Format Text tab of the ribbon. If you have a signature that’s automatically inserted into your replies, it won’t be automatically converted and will stay in plain text, so you’ll need either to right-click the signature in the message, or else click the Signature tool on the ribbon and choose the signature again, which changes the signature already in the message.
I’d only change the format of a reply if I needed the formatting capabilities of HTML mail to ensure my meaning was clear, and I was certain that the sender’s mail client can handle HTML, which requires knowledge that Outlook doesn’t provide – although perhaps it should.
One solution would be if Outlook remembered whether you’ve ever received an HTML mail from each particular address, and also what proportion of the mails you receive from that address are plain text. Your mail client could then know whether HTML was likely to be acceptable to the recipient and offer to switch from plain text to HTML to reply. Each user could adjust the thresholds for the Plain Text, Ask Me and HTML options, and you’d be able to choose either “if 90% or more of the mail from this sender is in Plain Text, then reply in Plain Text”, or “if I get 10% or less mail from this sender in Plain Text, then reply in HTML”, or “if I get more than 10%, but less than 90%, of mail from this sender in Plain Text, ask me for the reply format”.
That’s a lot of extra processing to do upon receiving every email, as well as an additional UI burden on users, and since most people wouldn’t even understand the questions, let alone the consequences of their choice, it might well be one more annoyance they could do without. On balance, it’s simpler to forbid “HTML replies only”.