SQL Query works different than expected - sql

Question

I have problems with understanding sql statement.
When I execute the it(see below), I'm getting only people with sgtn_typ 'L'.
SELECT DISTINCT kun_id kid
,dep_id
,ddg_rang_g RANG
,dep_perf_g
,TO_CHAR(dep_buchwert + dep_kasse, '999G999G990D99') WERT
,kun_name1
,Kun_vorname
,kun_cust_id
,kun_strasse
,kun_plz
,kun_ort
,kun_e_mail
,kun_pseudonym
,kka_value
FROM ddg, dep, kun, kat, kka, sgtn
WHERE dep_spi_id = 245
AND dep_abr_id = 24
AND ddg_dgr_id = 3
AND ddg_abr_id = dep_abr_id
AND ddg_spi_id = dep_spi_id
AND ddg_dep_id = dep_id
AND dep_kun_id = kun_id
AND kun_aktiv = 'J'
AND dep_spi_id = kun_spi_id
AND dep_id IS NOT NULL
AND dep_id NOT IN (SELECT ddg_dep_id
FROM ddg
WHERE ddg_spi_id = 245
AND ddg_abr_id = 0
AND ddg_dgr_id = 1)
AND kun_id = kka_kun_id
AND kka_spi_id = 245
AND kat_spi_id = 245
AND kka_kat_kuerzel = kat_kuerzel
AND kat_kuerzel = 'NSCH'
AND kka_spi_id = sgtn_spi_id
AND kka_kun_id = sgtn_kun_id
AND sgtn_spi_id = 245
AND sgtn_e_mail = kun_e_mail
AND (sgtn_typ = 'L'
OR (sgtn_typ = 'T'
AND sgtn_e_mail NOT IN (SELECT sgtn_e_mail
FROM sgtn
WHERE sgtn_spi_id = 245
AND sgtn_typ = 'L'))
)
ORDER BY kun_id, sgtn_typ;
But when I execute this, I'm getting people with sgtn_typ 'T':
SELECT *
FROM sgtn
WHERE sgtn_spi_id = 245
AND (sgtn_typ = 'L'
OR (sgtn_typ = 'T'
AND sgtn_e_mail NOT IN (SELECT sgtn_e_mail
FROM sgtn
WHERE sgtn_spi_id = 245
AND sgtn_typ = 'L'))
)
ORDER BY sgtn_kun_id;
I don't understand why? Could someone give me any clue? I was expecting, that I substitute all people with type 'L' and will get people with type 'T':
AND (sgtn_typ = 'L'
OR (sgtn_typ = 'T'
AND sgtn_e_mail NOT IN (SELECT sgtn_e_mail
FROM sgtn
WHERE sgtn_spi_id = 245
AND sgtn_typ = 'L'))
)
There are 'duplicates' in sgtn table(some people are entered with 'T' and 'L'). And apart from that the whole record is the same.
Table scheme are like the folowing:
SGTN:
SGTN_ID NUMBER(22)
SGTN_SPI_ID NUMBER(22)
SGTN_KUN_ID NUMBER(22)
SGTN_TYP VARCHAR2(4)
SGTN_GESCHLECHT VARCHAR2(4)
SGTN_VORNAME VARCHAR2(160)
SGTN_NAME1 VARCHAR2(240)
SGTN_STRASSE VARCHAR2(240)
SGTN_PLZ VARCHAR2(60)
SGTN_ORT VARCHAR2(240)
SGTN_E_MAIL VARCHAR2(240)
SGTN_GEB_DAT DATE(7)
SGTN_KLASSE VARCHAR2(200)
SGTN_SCHULE VARCHAR2(200)
SGTN_TELEFON VARCHAR2(120)
SGTN_KONTONUMMER VARCHAR2(120)
KUN:
KUN_ID NUMBER(22)
KUN_SPI_ID NUMBER(22)
KUN_LAN_ID NUMBER(22)
KUN_MED_KBEZ VARCHAR2(40)
KUN_NAME1 VARCHAR2(240)
KUN_MKZ VARCHAR2(80)
KUN_TS DATE(7)
KUN_AKTIV VARCHAR2(12)
KUN_KTOINH VARCHAR2(240)
KUN_BLZ VARCHAR2(40)
KUN_BANK VARCHAR2(240)
KUN_KTONR VARCHAR2(80)
KUN_ZAHLART VARCHAR2(4)
KUN_NAME2 VARCHAR2(240)
KUN_VORNAME VARCHAR2(160)
KUN_STRASSE VARCHAR2(240)
KUN_PLZ VARCHAR2(60)
KUN_ORT VARCHAR2(240)
KUN_TEL1 VARCHAR2(120)
KUN_TEL2 VARCHAR2(120)
KUN_FAX VARCHAR2(120)
KUN_E_MAIL VARCHAR2(240)
KUN_PSEUDONYM VARCHAR2(120)
KUN_PWD VARCHAR2(60)
KUN_CUST_ID VARCHAR2(240)
KUN_GESCHLECHT VARCHAR2(4)
KUN_K_NAME VARCHAR2(80)
KUN_K_NR NUMBER(22)
KUN_K_VALID VARCHAR2(40)
KUN_ZUSATZ_1 VARCHAR2(400)
KUN_ZUSATZ_DATUM DATE(7)
KUN_COMMENT VARCHAR2(4000)
KUN_EVT_SMS VARCHAR2(80)
KUN_EVT_E_MAIL VARCHAR2(240)
KUN_COMMENT2 VARCHAR2(4000)
KUN_AKTIV_BIS DATE(7)
KUN_FLG_AGB VARCHAR2(4)
KUN_TITEL VARCHAR2(200)
Thank you in advance for clues.
Greetings
R. Bada