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Folder locked by a POP3 session error

I’m having some problem with Pop3 connection. I have a windows service that cyclically checks a series of email accounts. Often I read in my logs this error:

AsposeException: Command failure.
—> AsposeException: Command failure.
—> AsposeException: Command failure.
—> Pop3Exception: Command failure.
_ at #=qSl$tZTRFBarbYz5wRD7e548K_5mO23$hAM_QPm$7BbjmqpfbrIWtkNA4Bs0VEwF.#=qGTDkgu6wvr7Flb5WIFBQyg==(Byte[] #=q2OJQJaghB3oqo9YEn_qOKA==, StringBuilder #=qw5r$wmg5bTsZIlTB4ZaGZQ==, Int32 #=qVo6HnceVPibZJcP$vpQpg==, Int32 #=qHIpk_I6k6wcXKOBkyepO0w==, Boolean #=qnl6IfhfW3SKumW8R7QrUcg==)
_ at #=qSl$tZTRFBarbYz5wRD7e548K_5mO23$hAM_QPm$7BbjmqpfbrIWtkNA4Bs0VEwF.#=q2o1rLJErpG58qbdwKI2jkw==(String #=qpqcNDss$KTyiQl3$nLhmylavrBQG0mdEoQ4sW8bFoWM=, Boolean #=qnl6IfhfW3SKumW8R7QrUcg==)
_ at #=qSl$tZTRFBarbYz5wRD7e548K_5mO23$hAM_QPm$7BbjmqpfbrIWtkNA4Bs0VEwF.#=qrbU4IhvlidS6OFLb6CYhKQ==()
— End of inner exception stack trace —
_ at #=qZjv$O8A8tC3xSHb2hmUzIx4l4QDqdIFYOx9AXqqvuk2A0mwyUrNaZoRI4T8g5grW.#=qVgz8W0fn8vufzrfJeqWjvA==(IAsyncResult #=qnoCi0w2uH1pECyhwRucoGw==)

_ at #=qZjv$O8A8tC3xSHb2hmUzIx4l4QDqdIFYOx9AXqqvuk2A0mwyUrNaZoRI4T8g5grW.#=qjM_ICd2OBlwpBCJmYYeTjw==()_
_ at #=qo8PzLFHvGls4$yHOTpw96uANTsWpC0bf8Rg823$fALgTF8Vyt5oTQpBb9HVHf8z8.#=qvingjrTCydadKJ4VRPP4x7JQnfv8daeiMP0QwMRqTzM=(String #=qHKYVJMEkIVM2p53RPZj0GQ==, Int32 #=qp90UqPu0KTpWNW1oKfMDQQ==, Int32 #=qw4OsrzMmP7FcEz0g4FxonA==)_
_ at #=qo8PzLFHvGls4$yHOTpw96uANTsWpC0bf8Rg823$fALgTF8Vyt5oTQpBb9HVHf8z8.#=qqh3tWKx160fvl5MrnvCTpA==(String #=qHKYVJMEkIVM2p53RPZj0GQ==, Int32 #=qp90UqPu0KTpWNW1oKfMDQQ==, Int32 #=qw4OsrzMmP7FcEz0g4FxonA==)_
_ at #=qo8PzLFHvGls4$yHOTpw96uANTsWpC0bf8Rg823$fALgTF8Vyt5oTQpBb9HVHf8z8.#=qdmp4FEnW50EjBobrEoozmHK6Dc4EVZSmYk7qqNWEnus=(String #=qHKYVJMEkIVM2p53RPZj0GQ==, Int32 #=qp90UqPu0KTpWNW1oKfMDQQ==)_
— End of inner exception stack trace —
_ at #=qo8PzLFHvGls4$yHOTpw96uANTsWpC0bf8Rg823$fALgTF8Vyt5oTQpBb9HVHf8z8.#=qdmp4FEnW50EjBobrEoozmHK6Dc4EVZSmYk7qqNWEnus=(String #=qHKYVJMEkIVM2p53RPZj0GQ==, Int32 #=qp90UqPu0KTpWNW1oKfMDQQ==)_
_ at #=qo8PzLFHvGls4$yHOTpw96uANTsWpC0bf8Rg823$fALgTF8Vyt5oTQpBb9HVHf8z8.#=qcW7kqa8dG3oXpjCQ$hdNW1vgKfy2aDU$JBnglRr0iE=.#=qR0$Xtdrb82mxKHNPerAGv5wCf3aU3Z06znM8X4CZHGrPTM$Votv0Ccyvrtmya20O()
— End of inner exception stack trace —
_ at #=qo8PzLFHvGls4$yHOTpw96uANTsWpC0bf8Rg823$fALgTF8Vyt5oTQpBb9HVHf8z8.#=qsEeOzLDn8Fz4p_oyMYowot3OcgpkokDOfInomlm2c84=(String #=qHKYVJMEkIVM2p53RPZj0GQ==, Int32 #=qp90UqPu0KTpWNW1oKfMDQQ==)_
_ at #=q3MqnJOy$uHE0Hjize6QO7Prd3QFsQM85rIzVHSBcaOo=.#=qnis9x60kJSDEXQxl1kQIuA==(Int32 #=qarDyfZt0bZalTZSKf2MqAA==)_
_ at Aspose.Email.Pop3.Pop3Client.GetMessageCount(IConnection iConnection, Boolean closeTransaction)_
_ at Aspose.Email.Pop3.Pop3Client.GetMessageCount()_

I have enabled the Pop3Client Activity Logging and in the log file the only error that I see is:

-ERR [SYS/PERM] folder locked by a POP3 session

Is it possible that every time that the activity log write this error, the Aspose Library throw the exception with the “command failure” message?
In what circumstances is the folder blocked by a POP3 session? Is it possible that it is due to concurrent access by other users or other applications?



Thank you for contacting Aspose support team.

I have tried to re-produce the scenario by connecting to mail server using POP3 Client but could not observe such issue. You may please share some console application which can be compiled and executed here to observe this issue. It will help us to analyze the problem and provide assistance accordingly. I am afraid that raising the exception while writing to LOG is not available.

This is server side error and I found some links where related information can be found. You may please have a look on these for more information about this error.

It is normal that you can’t replicate the problem. It depends on a particular email provider. Our customers use many different email providers and only one have that problem. We are trying to obtain a test account, but we still do not have it.
I don’t know under what circumstances it comes out and therefore I needed some technical details on your library to try to investigate better. The first thing I need to understand is if the exception that I have included in the previous post and that indicates the “command failure” error, can occur when there is the lock error that I have included in the activity log.
Then I should understand why there is that lock on the POP3 server, but if you’ve never had problems like that, I’ll try to investigate in another way.


It is like this that we haven’t come across any such failure earlier. Issues do occur but every issue has its own specific reason and we can’t deduce reason for one issue to be the same for other as well. In such case, we need a test account on the problematic email server to investigate the issue further. Please share it with us when you get hold of one where such issue arises. We’ll look into it for assisting you further.