Postfix: Receiving emails to an account works only if it aliased to itself

I have a Postfix email account [email protected] and the following two aliases:

mydomain.com     -> [email protected]   # catchall alias
[email protected] -> [email protected]

Now the second one looks silly but if I remove it, every email which is sent to [email protected] gets delivered to [email protected] even though (1) [email protected] is an account, (2) is enabled and (3) is not a send only account.

Why is the reception of any emails sent to this account only working if the alias to itself is enabled?

Here's my Postfix configuration:

inet_protocols = ipv4
mynetworks = 127.0.0.0/8
inet_interfaces = 127.0.0.1, x.x.x.x
myhostname = mail.mydomain.com
maximal_queue_lifetime = 1h
bounce_queue_lifetime = 1h
maximal_backoff_time = 15m
minimal_backoff_time = 5m
queue_run_delay = 5m
tls_preempt_cipherlist = yes
tls_ssl_options = NO_COMPRESSION
tls_high_cipherlist = EDH+CAMELLIA:EDH+aRSA:EECDH+aRSA+AESGCM:EECDH+aRSA+SHA256:EECDH:+CAMELLIA128:+AES128:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!DSS:!RC4:!SEED:!IDEA:!ECDSA:kEDH:CAMELLIA128-SHA:AES128-SHA
smtp_tls_security_level = dane
smtp_dns_support_level = dnssec
smtp_tls_policy_maps = mysql:/etc/postfix/sql/tls-policy.cf
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
smtp_tls_protocols = !SSLv2, !SSLv3
smtp_tls_ciphers = high
smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt
smtpd_tls_security_level = may
smtpd_tls_protocols = !SSLv2, !SSLv3
smtpd_tls_ciphers = high
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtpd_tls_cert_file=/etc/letsencrypt/live/mail.mydomain.com/fullchain.pem
smtpd_tls_key_file=/etc/letsencrypt/live/mail.mydomain.com/privkey.pem
smtpd_tls_dh1024_param_file=/etc/ssl/dh2048.pem
virtual_transport = lmtp:unix:private/dovecot-lmtp
smtpd_milters = inet:localhost:11332
non_smtpd_milters = inet:localhost:11332
milter_protocol = 6
milter_mail_macros =  i {mail_addr} {client_addr} {client_name} {auth_authen}
milter_default_action = accept
smtpd_relay_restrictions =      reject_non_fqdn_recipient
                                reject_unknown_recipient_domain
                                permit_mynetworks
                                reject_unauth_destination
smtpd_recipient_restrictions = check_recipient_access mysql:/etc/postfix/sql/recipient-access.cf
smtpd_client_restrictions =     permit_mynetworks
                                check_client_access
                                hash:/etc/postfix/without_ptr
                                reject_unknown_client_hostname
smtpd_helo_required = yes
smtpd_helo_restrictions =   permit_mynetworks
                            reject_invalid_helo_hostname
                            reject_non_fqdn_helo_hostname
                            reject_unknown_helo_hostname
smtpd_data_restrictions = reject_unauth_pipelining
mua_relay_restrictions = reject_non_fqdn_recipient,reject_unknown_recipient_domain,permit_mynetworks,permit_sasl_authenticated,reject
mua_sender_restrictions = permit_mynetworks,reject_non_fqdn_sender,reject_sender_login_mismatch,permit_sasl_authenticated,reject
mua_client_restrictions = permit_mynetworks,permit_sasl_authenticated,reject 
postscreen_access_list =        permit_mynetworks
                                cidr:/etc/postfix/postscreen_access
postscreen_blacklist_action = drop
postscreen_greet_action = drop
postscreen_dnsbl_threshold = 2
postscreen_dnsbl_sites =    ix.dnsbl.manitu.net*2
                            zen.spamhaus.org*2
postscreen_dnsbl_action = drop
virtual_alias_maps = mysql:/etc/postfix/sql/aliases.cf
virtual_mailbox_maps = mysql:/etc/postfix/sql/accounts.cf
virtual_mailbox_domains = mysql:/etc/postfix/sql/domains.cf
local_recipient_maps = $virtual_mailbox_maps
mailbox_size_limit = 0
message_size_limit = 52428800
biff = no
append_dot_mydomain = no
recipient_delimiter = +