Postfix bounces incoming emails with uppercase recipient (unknown user)

Question

I just installed Postfix on Debian minimum server and configured it as below:

installation:

1. installed it
2. chose internet site
3. set name to mydomainname.com

/etc/postfix/main.cf configs:

1. changed myhostname to mydomainname.com
2. changed alias_maps to virtual_alias_maps and set it to hash:/etc/postfix/virtual

/etc/postfix/virtual content:

(Shahab@eeePC is my local user with capital first letter!!)

1. add entry shahab@mydomainname.com Shahab
2. ran sudo postmap /etc/postfix/virtual
3. ran sudo service postfix restart

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I sent an email from gamil to shahab@mydomainname.com and here is the records of /var/log/mail.log:

    Sep  6 23:24:13 eeePC postfix/postfix-script[528]: warning: symlink leaves directory: /etc/postfix/./makedefs.out
Sep  6 23:24:13 eeePC postfix/postfix-script[564]: starting the Postfix mail system
Sep  6 23:24:13 eeePC postfix/master[566]: daemon started -- version 3.4.14, configuration /etc/postfix
Sep  6 23:26:56 eeePC postfix/smtpd[590]: warning: dict_nis_init: NIS domain name not set - NIS lookups disabled
Sep  6 23:26:57 eeePC postfix/smtpd[590]: connect from mail-qt1-f182.google.com[209.85.160.182]
Sep  6 23:26:58 eeePC postfix/smtpd[590]: C4BC2406C0: client=mail-qt1-f182.google.com[209.85.160.182]
Sep  6 23:26:58 eeePC postfix/cleanup[595]: C4BC2406C0: message-id=<CACR=pCMwDK+U_cLTVHsQFk+xmqtdJNZMzHe7M7CPtEn-SXBvGQ@mail.gmail.com>
Sep  6 23:26:58 eeePC postfix/qmgr[569]: C4BC2406C0: from=<mygmailaccount@gmail.com>, size=2512, nrcpt=1 (queue active)
Sep  6 23:26:58 eeePC postfix/local[596]: warning: dict_nis_init: NIS domain name not set - NIS lookups disabled
Sep  6 23:26:59 eeePC postfix/local[596]: C4BC2406C0: to=<Shahab@mydomainname.com>, relay=local, delay=0.33, delays=0.16/0.06/0/0.11, dsn=5.1.1, status=bounced (unknown user: "shahab")
Sep  6 23:26:59 eeePC postfix/cleanup[595]: 11188406CD: message-id=<20200906232659.11188406CD@mydomainname.com>
Sep  6 23:26:59 eeePC postfix/qmgr[569]: 11188406CD: from=<>, size=4322, nrcpt=1 (queue active)
Sep  6 23:26:59 eeePC postfix/bounce[597]: C4BC2406C0: sender non-delivery notification: 11188406CD
Sep  6 23:26:59 eeePC postfix/qmgr[569]: C4BC2406C0: removed
Sep  6 23:26:59 eeePC postfix/smtpd[590]: disconnect from mail-qt1-f182.google.com[209.85.160.182] ehlo=2 starttls=1 mail=1 rcpt=1 bdat=1 quit=1 commands=7
Sep  6 23:27:02 eeePC postfix/smtp[599]: 11188406CD: to=<mygmailaccount@gmail.com>, relay=gmail-smtp-in.l.google.com[74.125.143.27]:25, delay=3.3, delays=0.08/0/07/2.4/0.71, dsn=2.0.0, status=sent (250 2.0.0 OK  1599434822 k16si8490222ejd.738 - gsmtp)
Sep  6 23:27:02 eeePC postfix/qmgr[569]: 11188406CD: removed
Sep  6 23:30:19 eeePC postfix/anvil[593]: statistics: max connection rate 1/60s for (smtp:209.85.160.182) at Sep  6 23:26:57
Sep  6 23:30:19 eeePC postfix/anvil[593]: statistics: max connection count 1 for (smtp:209.85.160.182) at Sep  6 23:26:57
Sep  6 23:30:19 eeePC postfix/anvil[593]: statistics: max cache size 1 at Sep  6 23:26:57

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problem is Postfix can't recognize my user or something and removes the mail.