A friend sent me these Wonder Mail Passwords via text message. I’ve tried most of them (but not the Pokémon Red ones) and they seem to work.

Getting MD Red-exclusive Pokémon in MD Blue:

Porygon:
Rescue in Thunderwave Cave B4F (E-rank)

1?58 T5+? 4J78
WS?7 F??R NQ?X

Mantine:
Escort Kirlia to Tiny Woods B3F (D-rank)

4??N 22…? ?Q6J
H3?♂ 8470 JN?W

Plusle:
Escort Minun to Thunderwave Cave B5F (D-rank)

F?RP F?…? 4+7?
…R?H 64?0 R???

Roselia:
Rescue in Tiny Woods B2F (E-rank)

F?4N +WT? ?+6N
FR?J F?66 85?W

Feebas:
Deliver Cheri Berry to Grand Sea B9F (B-rank)

X?7P ♀?+? ?XP6
RJ?Q FJC5 ?W??

Milotic:
Escort Quilava to Thunderwave Cave B3F (D-rank)

1?N9 X3+? ?+65
+!?Q +470 S0?W

Getting MD Blue-exclusive Pokémon in MD Red:

Magikarp:
Rescue from Stormy Sea B12F (B-rank)

X??S ??X? 468?
♀+?? 9756 SY??

Lapras:
Rescue in Tiny Woods B2F (E-rank)

F?J? 690? 4Q6C
C!?? 8?66 8Q?♀

Aipom:
Deliver Radar Orb to Silent Chasm B5F (D-rank)

4?RC W♂T? ?076
FM?Y 24?5 +N?W

Porygon2:
Rescue in Tiny Woods B2F (E-rank)

F?5N -QF? ?+6!
?H?? F?6R 69?W

Minun:
Escort to Mt Blaze 7F (B-rank)

4?M9 FQX? 28N7
HR?H P5?0 !4?W

Friend Areas:

Boulder Cave:
Rescue Oddish in Sinister Woods 8F (D-rank)

P?2Y J1T? 4HPC
K1?+ 0?56 64?W

Dragon Cave:
Escort Phanpy to Thunderwave Cave B3F (D-rank)

H?08 ?9S? ?Q64
?P?! 84S0 +F?!

Mt Moonview:
Escort Voltorb to Tiny Woods B3F (D-rank)

0?0N M1S? ?06♀
N2?Y F4+0 NP?W

Sky Blue Plains:
Escort Baltoy to Tiny Woods B3F (D-rank)

2?0N 13+? ?36R
MT?R 8420 MX?W

Rescue Team HQ Statues:

Weavile:
Escort Poliwhirl to Northern Range (Zubat) 24F (S-rank)

1?NK ♂♂F? 4SS9
MF?+ CNN0 JX?W

Mime Jr:
Escort Salamence to Pitfall Valley (Mr Mime) 19F (S-rank)

F?C4 FHT? 440P
M-?♂ 2CN0 JX?+

Additional Dungeons:

(All are Jigglypuff asking to rescue AYR in Level 1 of said dungeon and are B-rank):
Oddity Cave:

??MS CJ…? 44?P
MF?8 7J6R …M?1

Remains Island:

??M4 CJY? 44?P
CF?8 7J6R …M?1

Marvellous Sea:

??MH CJ…? 44?P
CF?8 7J6R …M?1

Fantasy Strait:

??M1 CJY? 44?P
HF?8 7J6R …M?1

---

Explorers of Sky—Sun Ribbon:

Rescue Oddish from Crystal Cave B6F (S-rank)

F#@13 5QC2CF9 278QR
XQN+4 WQ8PSY2 WWHPT

Explore with Magikarp to Concealed Ruins B15F (*5-rank)

2XF=K #9N&XKR Y9F+R
58Y-8 8MRR6#& OFF#T

Prospect with Electabuzz to Surrounded Sea B17F (*6-rank)

40TP- 4Y-&38W FXXX6
N3RKY 7SJ7X2% &TK15