The subject line of an email should be brief yet descriptive. After all, it is by scanning subject lines that many people will find your message among the slew of other incoming messages competing for their attention.
Suppose you send two colleagues an email with an attachment—a report about technology expenses for the third quarter of 2023. This is not enough of a subject line:
Subject: Technology Report
That blandly labeled email will easily be lost amid all the other technology report emails. This doesn't work either:
Subject: Report on technology expenses for the third quarter of 2023 attached
This time the subject line is too long and meandering. If your subject is wordy, it will be more difficult for recipients to read it quickly, and it is also possible that their devices will be too small to display all the text at once.
This next version is both precise and concise:
Subject: Technology Expense Report Q3 2023
This version is superior to the previous two options. Any readers will quickly understand exactly what they are receiving.
Regarding capitalization of your subject line, you have multiple choices. Naturally you should always capitalize proper nouns such as Joan or Empire State Building, but for the rest of the words in your subject, you can choose between the following options:
The first capitalization option can give email subject lines a more polished, professional appearance, but it's really up to you. For long subject lines, initial capital letters throughout can be overwhelming; in such cases, a better choice may be to capitalize only the first word and any proper nouns.
Subjects with no capital letters at all generally don’t look as polished as the two options described above.