Dan Mosedale, a programmer for the open-source email software, published the date in a Thunderbird schedule draft he announced on Thursday.
"If we're lucky, we relabel 3.1RC1 [release candidate 1] as final and ship it on Tuesday, 6 April. Otherwise, there's an RC2," Mosedale said in the planning document.
For more, read "Mozilla hopes to finish Thunderbird 3.1 in April" on CNET News.