Hello Member,
The best options are mentioned below.
1. Purchase English grammar book or prefer online websites because if you will ignore little mistake in E - mail , it will give bad impression to your client.
2. The other option is hire a professional person whose English is very strong and ( positive extra ordinary ) who is capable to speak and write excellent English.
And also follow some important points
Make your purpose clear
Brand with a meaningful subject line.
Front-load the nuts and bolts.
Pay attention to tone
Engage people with your sentences
Vary sentence length
Don't be a pompous jerk
Brevity Is key.
CC with moderation.
Thanks