Informal ways of beginning/ending an e-mail
In Chinese culture, politeness is never too much only except for between really intimate friends or lovers. Especially when getting along with an elderly person, it's a good idea to keep being formal and polite until you're completely certain that it's not necessary.
This link explains the conventions very well. To cite the essence of it,

2 ．问候语
　　第二行开头空两格写问候语。
　　运用礼貌语言，使收信人感到亲切，受到尊敬。
　　长者多问候身体，中年人多问候事业和家庭，青年人多问候爱情和学业，少年儿童多祝愿健康成长。
4 ．结尾
　　要根据收信人的身份，写表示祝愿的话，以示礼貌。
　　一般性的祝词“此致”“敬礼”，格式是另起一行空两格写“此致”，“敬礼”下一行顶格写。
　　给长者的信往往写“祝您健康长寿”，给朋友写“祝工作顺利”，给晚辈写“祝你学习进步”。

When in doubt, be as polite as possible. When I feel obligated by the culture, I would simply use formulaic 您好 as 问候语 and 此致敬礼 as 结尾.
Edit:
Adding translation for the citation with my editorial in parenthesis. The translation is done in a kinda verbatim way in order to preserve the sense of the culture, although it may sound unnatural in English.

2 . Greetings
Greetings should be placed on the second line ( the first line is a title) with an indentation of two spaces.
Use polite language to make the recipient feel warm and respected.
For elderly recipients, send regards to health; for middle-aged people, career and family; for a young person, love life (only appropriate if the sender is an elder to the recipient) and studying; for children, health and striving.
4 . Ending
To show politeness, use some blessing words based on who the recipient is (social status and relationship to the sender).
A general one is “此致”“敬礼” (usage similar to &quot;best regards&quot; in English, literal translation should be &quot;hereby, salute&quot;). The format convention is to put &quot;此致&quot; on a new line with an indentation of two spaces and &quot;敬礼&quot; on the next line without indentation.
People usually say &quot;祝您健康长寿” (wish you health and longevity) to elderly people, &quot;祝工作顺利&quot; (wish you a successful career) to friends and &quot;祝学习进步&quot; (wish you good progress in studies) to the younger generation.