Personalized subject lines in e-mail marketing messages for Mother’s Day can significantly boost transaction rates. And while a sense of urgency in those e-mails can also increase sales, such pressure may prove redundant as the May 12 commemoration nears, according to Experian Marketing Services.

In a report about ways to improve Mother’s Day e-mail marketing, Experian says that while retailers typically begin sending those messages in early April, 46% of Mother’s Day e-mail volume is sent within a week of the holiday. The report suggests that relatively few consumers are buying well before Mother’s Day, as campaigns sent in the two weeks before the holiday account for 80% of the transactions and 75% of the revenue stemming from the occasion.

Giving those e-mails a sense of urgency, however, can spark sales—but only to a point, Experian says. Subject lines that promote sales with such terms as “last day,” “final hours” and “today only” have approximately double the transaction rates of other Mother’s Day e-mails, but only during April and the beginning of May. During the week or so before the holiday, those types of subject lines produce no large increase in transaction rates. “It appears the pressure to buy something for Mom is strong enough that urgency words in subject lines may not be needed,” the report says.

Another factor that encourages Mother’s Day transactions are personalized subject lines, Experian says. They increase open rates by 54% and transaction rates by 66% compared to e-mails without those types of subject lines. Putting offers into subject lines increases transactions rates by 32% and revenue per e-mail by 15%, Experian says. Putting free shipping or free gift offers in subject lines increases transactions by 30% and revenue by 25%.