If you have Japanese customers that you do business with you may have been thinking about them recently and wondered what would be suitable to say at this time.
As everyone is very busy at the moment thinking about family, friends, loved ones and colleagues a short message expressing sympathy may be of comfort.
When sending an email at this time please remember that as people are currently very busy (physically and mentally) they will most certainly read your message but may not respond. Don't be too worried about this. Your point is to communicate with them.
Japanese
この度の地震により被災された皆様に、心よりお見舞い申し上げます。
一日も早い復旧・復興を心からお祈り申し上げます。
English - translation
To everyone affected by the earthquake at this time, I would like to express sincere sympathy.
We sincerely hope early recovery and reconstruction.
We sincerely hope early recovery and reconstruction.
You may want to include both the Japanese and English translation. The English translation may be useful for your Japanese colleague to help form a short English reply.
As mentioned don't worry if you do not get a reply, they will read it.