The people who answer questions here, are other users volunteering their time (like me), not Mozilla employees or Thunderbird developers. As a suggestion for the future, volunteers tend to avoid questions where people want to talk about what they authorized or approved of. That is not relevant to the problem, but it does lead us to think if we reply we are inviting conflict. Additionally we know exactly what you tell us about you, your problem and your computing environment. In your case we still know nothing except you only have the last two months emails. SO we are left to guess and rely on past experience as to what might be the cause. As you specifically mention 2 months, I would guess you have configured an IMAP account and your mail provider has a retention policy of 2 months on how long you can keep old mail on the server or without formally archiving or in some other way removing it from their server. I did however say it was a guess. I do not know who your mail provider is, how you configured your account or what other software you might have installed on your machine or another device like a phone that is relevant. Another common cause of mail being only for a period of time in Thunderbird is a phone mail application that deleted it after so long because phone storage is limited